<PAGE>


                           ACADIA PHARMACEUTICALS INC.


                ________________________________________________



                   AMENDED AND RESTATED STOCKHOLDERS AGREEMENT


                ________________________________________________



                                   MAY 5, 2000



<PAGE>

                                                   TABLE OF CONTENTS

<TABLE>
<CAPTION>

                                                                                                               PAGE
<S>                                                                                                            <C>
ARTICLE 1         DEFINITIONS.....................................................................................2

ARTICLE 2         RIGHT OF FIRST REFUSAL..........................................................................2

         2.1      Generally.......................................................................................2

         2.2      Acceptance......................................................................................3

         2.3      Sale by Company.................................................................................3

         2.4      Decrease in Shares Sold.........................................................................3

         2.5      Purchase of Shares..............................................................................4

         2.6      Shares not Sold.................................................................................4

         2.7      Exclusions from First Refusal Right.............................................................4

         2.8      Applicability of this Agreement to Offered Securities...........................................5

ARTICLE 3         RESTRICTIONS ON TRANSFER........................................................................5

         3.1      Generally.......................................................................................5

         3.2      [Intentionally Omitted].........................................................................5

         3.3      Permitted Transfers.............................................................................5

         3.4      Offer for Sale; Notice of Proposed Sale.........................................................6

         3.5      Option to Purchase..............................................................................6

         3.6      Sale to Offerer; Closing........................................................................7

         3.7      Co-Sale Rights..................................................................................8

         3.8      Treatment of Sale Proceeds......................................................................8

ARTICLE 4         COME-ALONG OBLIGATIONS..........................................................................8

         4.1      Generally.......................................................................................8

         4.2      Notice..........................................................................................9

         4.3      Closing.........................................................................................9

         4.4      Stock Options..................................................................................10

ARTICLE 5         EVENTS OF DEFAULT..............................................................................10

         5.1      Events of Default..............................................................................10

         5.2      Remedies on Default............................................................................11

         5.3      Notice of Default..............................................................................11

         5.4      Specific Enforcement...........................................................................11

         5.5      Remedies not Waived............................................................................11


                                                         i.

<PAGE>

                                                   TABLE OF CONTENTS
                                                     (CONTINUED)

ARTICLE 6         GOVERNANCE.....................................................................................12

         6.1      Composition of the Board.......................................................................12

         6.2      Frequency, Quorum and Voting...................................................................13

         6.3      Notice of Meetings.............................................................................13

         6.4      Special Meetings...............................................................................13

         6.5      Composition of Committees......................................................................13

         6.6      Governance of Subsidiaries.....................................................................13

         6.7      Stockholders' Obligations to Take Certain Actions..............................................13

         6.8      Limitation on Directors' Actions...............................................................13

ARTICLE 7         AFFIRMATIVE COVENANTS OF THE COMPANY...........................................................14

         7.1      Material Changes and Litigation................................................................14

         7.2      Transactions with Affiliates...................................................................14

         7.3      Board Observer.................................................................................14

         7.4      Corporate Existence............................................................................14

         7.5      Financial Statements and Other Information.....................................................14

         7.6      Inspection of Books and Records................................................................15

         7.7      Payment of Taxes...............................................................................15

         7.8      Insurance......................................................................................15

         7.9      Patents and Intellectual Property..............................................................15

         7.10     Nondisclosure Agreements.......................................................................16

         7.11     Expenses and Compensation of Directors.........................................................16

         7.12     Reservation of Common Stock....................................................................16

         7.13     International Investment and Trade in Services Survey Act......................................16

         7.14     Copenhagen Lead Discovery Project..............................................................16

         7.15     Notice of Certain Breaches.....................................................................16

         7.16     Budgets........................................................................................16

         7.17     Conduct of Business............................................................................16

         7.18     Preservation of Shares.........................................................................16

ARTICLE 8         NEGATIVE COVENANTS.............................................................................17

ARTICLE 9         REGISTRATION RIGHTS............................................................................17


                                                         ii.

<PAGE>

                                                   TABLE OF CONTENTS
                                                     (CONTINUED)

         9.1      Required Registrations.........................................................................17

         9.2      Incidental Registration........................................................................18

         9.3      Registration Procedures........................................................................19

         9.4      Allocation of Expenses.........................................................................20

         9.5      Indemnification and Contribution...............................................................21

         9.6      Indemnification With Respect to Underwritten Offering..........................................23

         9.7      Information by Holder..........................................................................23

         9.8      "Stand-Off" Agreement..........................................................................23

         9.9      Rule 144 Requirements..........................................................................23

         9.11     Termination of Registration Rights.............................................................24

         9.12     Transfers of Rights............................................................................24

         9.13     Registration Rights to Third Parties...........................................................24

         9.14     Construction...................................................................................24

ARTICLE 10        DEFINITIONS....................................................................................25

ARTICLE 11        GENERAL PROVISIONS.............................................................................31

         11.1     Legends........................................................................................31

         11.2     Amendment; Termination.........................................................................32

         11.3     Effect of Agreement............................................................................32

         11.4     Computation of Percentages or Pro Rata Share...................................................32

         11.5     Counterparts...................................................................................32

         11.6     Notices........................................................................................32

         11.7     Entire Agreement...............................................................................32

         11.8     Governing Law..................................................................................33

         11.9     Severability...................................................................................33

         11.10    Construction...................................................................................33

         11.11    Arbitration....................................................................................33
</TABLE>

                                                       iii.

<PAGE>


                           ACADIA PHARMACEUTICALS INC.

                   AMENDED AND RESTATED STOCKHOLDERS AGREEMENT


         THIS AMENDED AND RESTATED STOCKHOLDERS AGREEMENT is entered into as of
May 5, 2000, by and among ACADIA PHARMACEUTICALS INC., a Delaware corporation
(the "Company"), those individuals and entities identified on the signature page
hereof as the "Existing Institutional Stockholders" (individually, each an
"Existing Institutional Stockholder" and collectively, the "Existing
Institutional Stockholders"), MARK R. BRANN (the "Founding Stockholder") and the
entities identified on the signature page hereof as the "New Institutional
Stockholders" (individually, each a "New Institutional Stockholder" and
collectively, the "New Institutional Stockholders"). Each of the Existing
Institutional Stockholders and New Institutional Stockholders are sometimes
referred to herein as an "Institutional Stockholder" or collectively as
"Institutional Stockholders." Each of the Institutional Stockholders and the
Founding Stockholder are sometimes referred to as "Stockholder" and are
collectively referred to as the "Stockholders."

                                    RECITALS

         A. The parties to this Agreement are the Company and certain holders of
the issued and outstanding capital stock of the Company.

         B. The Company, the Founding Stockholder and the First Institutional
Stockholders entered into a Stockholders Agreement, dated as of February 3, 1997
(the "First Stockholders Agreement") in connection with the purchase and sale of
Series A Preferred Stock of the Company.

         C. On August 12, 1997 the parties to the First Stockholders Agreement
and the Partnership amended the First Stockholders Agreement (the "First Amended
Stockholders Agreement") in connection with the purchase and sale of the Series
B Preferred Stock of the Company.

         D. On September 24, 1997, the parties to the First Amended Stockholders
Agreement amended the First Amended Stockholders Agreement (the "Second Amended
Stockholders Agreement") in connection with the Company's sale of Series C
Preferred Stock to Vision Pharmaceuticals L.P.

         E. On August 26, 1998, the Parties to this Agreement other than the New
Institutional Investors amended the Second Amended Stockholders Agreement (the
"Third Amended Stockholders Agreement") in connection with the purchase and sale
of the Series D Preferred Stock of the Company.

         F. In connection with the issuance and sale of Series E Preferred Stock
by the Company, the parties to the Third Amended Stockholders Agreement and the
New Institutional Investors wish to amend and restate the Third Amended
Stockholders Agreement.


                                       1.

<PAGE>

         G. Certain of the Existing Institutional Stockholders own shares of
Series A Preferred Stock of the Company, certain of the Existing Institutional
Stockholders own shares of Series B Preferred Stock of the Company, certain of
the Existing Institutional Stockholders own Shares of Series D Preferred Stock
of the Company, and certain of the Existing Institutional Stockholders and New
Institutional Stockholders own shares of Series E Preferred Stock of the
Company. Certain of the Stockholders also hold warrants to purchase Common Stock
of the Company. The Founding Stockholder and certain of the Existing
Institutional Stockholders own shares of Common Stock.

         H. The Stockholders believe that it is in the best interests of the
Company and the Stockholders to (i) provide that Stock shall be transferable
only upon compliance with the terms hereof; (ii) provide certain registration
rights to the Existing Institutional Stockholders and the New Institutional
Stockholders; and (iii) set forth their agreements on certain other matters.

         NOW, THEREFORE, the parties hereto agree as follows:

                                    ARTICLE 1

                                   DEFINITIONS

         Capitalized terms used herein shall have those meanings ascribed to
them in Article 10 of this Agreement.

                                    ARTICLE 2

                             RIGHT OF FIRST REFUSAL

         2.1 GENERALLY. Subject to Section 2.7 below, the Company shall not
issue, sell or exchange, agree to issue, sell or exchange, or reserve or set
aside for issuance, sale or exchange, (i) any Stock, (ii) any other equity
securities of the Company, (iii) any option, warrant or other right to subscribe
for, purchase or otherwise acquire any equity securities of the Company, or (iv)
any debt securities convertible into capital stock of the Company (collectively,
unless excluded by Section 2.7 below, the "Offered Securities"), unless in each
such case the Company shall have first complied with this Agreement. The Company
shall deliver to each Stockholder a written notice of any proposed or intended
issuance, sale or exchange of Offered Securities (the "Offer"), which Offer
shall (i) identify and describe the Offered Securities, (ii) describe the price
and other terms upon which they are to be issued, sold or exchanged, and the
number or amount of the Offered Securities to be issued, sold or exchanged,
(iii) identify the persons or entities to which or with which the Offered
Securities are to be offered, issued, sold or exchanged, and (iv) offer to issue
and sell to or exchange with such Stockholder (A) such portion of the Offered
Securities as the aggregate number of shares of the Common Stock of such
Stockholder (treating, for this purpose, any outstanding convertible capital
stock on an "as converted" basis and, with respect to any outstanding Preferred
Stock, taking into account that number of shares of Preferred Stock to which
that Stockholder would be entitled following the declaration and issuance of the
"Special Dividend" as set forth in the Certificate) bears to the total number of
shares of Common Stock outstanding (after giving effect to such conversion and
dividend) (the "Basic Amount"), and (B) any additional portion of the Offered
Securities as such Stockholder


                                      2.

<PAGE>

shall indicate it will purchase or acquire should the other Stockholders
subscribe for less than their Basic Amounts (the "Undersubscription Amount"),
PROVIDED that the Undersubscription Amount shall be subject to reduction as
set forth in Section 2.2 below. Each Stockholder shall have the right, for a
period of forty-five (45) days following delivery of the Offer, to purchase
or acquire, at a price and upon other terms specified in the Offer, the
number of Offered Securities described above. The Offer by its term shall
remain open and irrevocable for such forty-five (45) day period.

         2.2 ACCEPTANCE. To accept an Offer, in whole or in part, a Stockholder
must deliver a written notice to the Company prior to the end of the forty-five
(45) day period of the Offer, setting forth the portion of the Stockholder's
Basic Amount that the Stockholder elects to purchase and, if the Stockholder
shall elect to purchase all of its Basic Amount, the Undersubscription Amount
(if any) that the Stockholder elects to purchase (the "Notice of Acceptance").
If the Basic Amounts subscribed for by all Stockholders are less than the total
Offered Securities, then any Stockholder who has set forth Undersubscription
Amounts in its Notice of Acceptance shall be entitled to purchase, in addition
to the Basic Amounts subscribed for, all Undersubscription Amounts it has
subscribed for; PROVIDED, HOWEVER, that should the Undersubscription Amounts
subscribed for exceed the difference between the Offered Securities and the
Basic Amounts subscribed for (the "Available Undersubscription Amount"), each
Stockholder who has subscribed for any Undersubscription Amount shall be
entitled to purchase only that portion of the Available Undersubscription Amount
as the Undersubscription Amount subscribed for by such Stockholder bears to the
total Undersubscription Amounts subscribed for by all Stockholders, subject to
rounding by the Board of Directors to the extent it reasonably deems necessary.

         2.3 SALE BY COMPANY. In the event that Notices of Acceptance are not
given by Stockholders in respect of all the Offered Securities, the Company
shall have up to 120 days from the expiration of the period set forth in Section
2.1 above to issue, sell or exchange all or any part of such Offered Securities
as to which a Notice of Acceptance has not been given by the Stockholders (the
"Refused Securities"), but only to one or more of the offerees or purchasers
described in the Offer and only upon terms and conditions (including, without
limitation, unit prices and interest rates) which are not more favorable, in the
aggregate, to the acquiring person or persons or less favorable to the Company
than these set forth in the Offer.

         2.4 DECREASE IN SHARES SOLD. In the event the Company shall propose to
sell less than all the Refused Securities (any such sale to be in the manner and
on the terms specified in Section 2.3 above), then each Stockholder may, at its
sole option and in its sole discretion, reduce the number or amount of the
Offered Securities specified in its Notice of Acceptance to an amount that shall
be not less than the number or amount of the Offered Securities that the
Stockholders elected to purchase pursuant to Section 2.2 above multiplied by a
fraction, (i) the numerator of which shall be the reduced number or amount of
Offered Securities the Company proposes to issue, sell or exchange (including
Offered Securities to be issued or sold to Stockholders pursuant to Section 2.2
above prior to such reduction) and (ii) the denominator of which shall be the
amount of all Offered Securities. In the event that any Stockholder so elects to
reduce the number or amount of Offered Securities specified in its Notice of
Acceptance, the Company may not issue, sell or exchange more than the reduced
number or amount of the


                                     3.

<PAGE>

Offered Securities unless and until such securities have again been offered
to the Stockholders in accordance with Section 2.1 above.

         2.5 PURCHASE OF SHARES. Upon the closing of the issuance, sale or
exchange of all or less than all the Refused Securities, the Stockholders shall
acquire from the Company, and the Company shall issue to the Stockholders, the
number or amount of Offered Securities specified in the Notices of Acceptance,
as reduced pursuant to Section 2.4 above if the Stockholders have so elected,
upon the terms and conditions specified in the Offer. The purchase by the
Stockholders of any Offered Securities is subject in all cases to the
preparation, execution and delivery by the Company and each Stockholder of a
purchase agreement relating to such Offered Securities reasonably satisfactory
in form and substance to each Stockholder and their respective counsel.

         2.6 SHARES NOT SOLD. Any Offered Securities not acquired by the
Stockholders or other persons in accordance with Section 2.3 above may not be
issued, sold or exchanged until they are again offered to the Stockholders under
the procedures specified in this Agreement.

         2.7 EXCLUSIONS FROM FIRST REFUSAL RIGHT. The rights of the Stockholders
under Sections 2.1 through 2.6, inclusive, shall not apply to, and the
securities described shall not be deemed "Offered Securities" for:

                  (a) Common Stock issued as a stock dividend to holders of
Common Stock or upon any subdivision or combination of shares of Common Stock;

                  (b) the issuance of any shares of Stock to holders of
Preferred Stock, pursuant to the provisions of the Certificate;

                  (c) the issuance of shares of Common Stock, or options
exercisable therefor, including options outstanding on the date of this
Agreement (as such number may be proportionately adjusted in the event of any
stock splits, stock dividends, recapitalization or similar events occurring on
or after the date of this Agreement) issued or issuable to employees, officers
or directors of, or consultants or advisers to the Company pursuant to stock
purchase or stock option plans or similar arrangements approved by the Board of
Directors;

                  (d) the issuance of Common Stock pursuant to the exercise of
Warrants outstanding as of the date hereof;

                  (e) securities issued solely in consideration for the
acquisition (whether by merger or otherwise) by the Company or any of its
subsidiaries of all or substantially all of the stock or assets of any other
entity;

                  (f) shares of Common Stock sold by the Company in an
underwritten public offering pursuant to an effective registration statement
under the Securities Act, resulting in at least Seven Million Five Hundred
Thousand United States Dollars (US$7,500,000) of gross proceeds to the Company
at a minimum price of seven dollars and 50 cents ($7.50) per share (subject to
appropriate adjustment for stock splits, stock dividends, recapitalizations and
other similar events) (a "Qualifying IPO");


                                      4.

<PAGE>

                  (g) securities issued in connection with bona fide strategic
transactions involving the Company and other entities, including (i) joint
ventures, manufacturing, marketing or distribution arrangements or (ii)
collaboration or technology transfer arrangements; PROVIDED that each such
strategic transaction and the issuance of shares pursuant thereto, has been
approved by the Board of Directors and the arrangement involves diligence
obligations (if applicable);

                  (h) securities issued in connection with the Company entering
into an equipment leasing arrangement or debt financing from a bank or similar
financial institution; PROVIDED, HOWEVER, that such issuances shall not exceed
or be exercisable for or convertible into more than an aggregate of 25,000
shares of capital stock of the Company (subject to appropriate adjustment for
stock splits, stock dividends, recapitalizations and other similar events); or

                  (i) shares of Series E Preferred Stock purchased under the
Series E Stock Purchase Agreement.

         2.8 APPLICABILITY OF THIS AGREEMENT TO OFFERED SECURITIES. No issuance
or sale of Offered Securities shall be valid unless the purchaser of such
Securities shall have executed and delivered a counterpart of this Agreement.
Offered Securities issued, sold or exchanged pursuant to this Agreement,
including those to which Section 2.7(a), (b), (d) and (e) of this Agreement is
applicable, shall be subject to the terms of this Agreement, PROVIDED, HOWEVER,
that shares of Common Stock which are the subject to the Company's 1997 Stock
Option Plan shall not be subject to this Agreement.

                                    ARTICLE 3

                            RESTRICTIONS ON TRANSFER

         3.1 GENERALLY. Any sale or other disposition of any of the shares of
Stock by a Stockholder, other than according to the terms of this Agreement,
shall be void and transfer no right, title or interest in or to any of such
shares of Stock to the purported transferee. Moreover, no transfers shall be
valid unless and until the transferee shall have executed and delivered a
counterpart of this Agreement.

         3.2 [INTENTIONALLY OMITTED].

         3.3 PERMITTED TRANSFERS. Subject to Section 3.1 of this Agreement, (a)
a Stockholder may sell, assign or transfer, without compliance with Sections 3.4
through 3.6 of this Agreement, any or all of his shares of Stock to an Affiliate
of such Stockholder or to his spouse or children or to a trust established for
the benefit of his spouse, children or himself, or dispose of them under his
will or pursuant to a judicial decree or order (PROVIDED that, in each such
case, the Company receives written notice of such transfer, that this Agreement
shall be binding upon each such transferee and, prior to the completion of such
transfer, each transferee or his or her legal representative shall have executed
documents assuming the obligations of the transferring Stockholder under this
Agreement with respect to the transferred shares). Notwithstanding the
foregoing, in the event of any sale, assignment or transfer pursuant to this
Section 3.3 the transferor and the transferee(s) shall be jointly and severally
liable as one


                                      5.

<PAGE>

Stockholder pursuant to this Agreement. The pledge of any shares of Stock
shall be permitted only with the approval of the Board of Directors, in its
sole discretion.

         3.4 OFFER FOR SALE; NOTICE OF PROPOSED SALE. If any Stockholder (the
"Transferring Party") desires to sell, transfer or otherwise dispose of any of
his shares of Stock, or of any interest in such shares of Stock, whether
voluntarily or by operation of law, in any transaction other than pursuant to
Section 3.3 of this Agreement, such Transferring Party shall first deliver
written notice of such desire to do so (the "Notice") to the other Stockholders
and the Company (such other Stockholders referred to herein as the
"Non-Transferring Parties"), in each case in the manner prescribed in Section
11.6 of this Agreement. The Notice shall specify: (i) the name and address of
the party to which the Transferring Party proposes to sell or otherwise dispose
of the Stock or interest in the Stock (the "Offerer"), (ii) the number of shares
of Stock the Transferring Party proposes to sell or otherwise dispose of (the
"Shares Proposed for Transfer"), (iii) the consideration per share of Stock
offered by the Offerer to the Transferring Party for the proposed sale, transfer
or disposition, and (iv) all other material terms and conditions of the proposed
transaction. The Notice shall be accompanied by a copy of the offer from the
Offerer to the Transferring Party or such other evidence of the offer that is
reasonably satisfactory to the Transferring Parties.

         3.5 OPTION TO PURCHASE.

                  (a) The Stockholders and the Company shall have the option to
purchase all but not less than all of the Shares Proposed for Transfer. The
Stockholders shall have the first option (the "First Option") to purchase all or
any part of the Shares Proposed for Transfer for the consideration per share and
on the terms and conditions specified in the Notice. The First Option must be
exercised no later than forty-five (45) days after such Notice is deemed under
Section 11.6 hereof to have been delivered. The Stockholders shall have a right
to purchase the Shares Proposed for Transfer on a pro rata basis according to
the number of shares of Stock owned by such Stockholders. Such option shall be
exercised by delivery of written notice to the Secretary of the Company.

                  (b) In the event options to purchase have been exercised by
the Non-Transferring Parties with respect to some but not all of the Shares
Proposed for Transfer, those Non-Transferring Parties who have exercised their
options within the forty-five (45) day period specified in Section 3.5(a) shall
have an additional option, for a period of fifteen (15) days next succeeding the
expiration of such forty-five (45) day period, to purchase all or any part of
the balance of such Shares Proposed for Transfer on the terms and conditions set
forth in the Notice, which option shall be exercised by the delivery of written
notice to the Secretary of the Company. In the event there are two or more such
Non-Transferring Parties that choose to exercise the last-mentioned option for a
total number of shares of Stock in excess of the number available, the shares of
Stock available for each such Non-Transferring Party's option shall be allocated
pro rata based on the number of shares of Stock owned by the Non-Transferring
Parties so electing.

                  (c) In the event the Non-Transferring Parties do not exercise
their option with respect to all of the Shares Proposed for Transfer within such
fifteen (15) day period, the Company may elect within eight (8) days succeeding
the expiration of such fifteen (15) day


                                      6.

<PAGE>

period, to purchase the Shares Proposed for Transfer not purchased by the
Stockholders (the "Remaining Shares"). In such case the Company shall deliver
written notice of such purchase to the Transferring Party.

                  (d) If the options to purchase the Shares Proposed for
Transfer are exercised in full by the Non-Transferring Parties and/or the
Company, the Secretary of the Company shall immediately notify all of the
exercising Non-Transferring Parties of that fact.

                  (e) In the event the Non-Transferring Parties and/or the
Company duly exercise their option to purchase the Shares Proposed for Transfer,
the closing of such purchase shall take place at the offices of the Company on a
single date agreed to among such purchasers, which date shall be not later than
sixty (60) days after the expiration of the applicable relevant period pursuant
to Section 3.5(a)-(c) above.

                  (f) To the extent that the consideration proposed to be paid
by the Offerer for the Shares Proposed for Transfer consists of property other
than cash or a promissory note, the consideration required to be paid by the
Company and/or the Non-Transferring Parties exercising their option to purchase
may consist of cash equal to the value of such property, as determined in good
faith by agreement of the Transferring Party and the Company and/or the
Non-Transferring Parties acquiring such Shares Proposed for Transfer. In the
event that the parties are not able to determine the value of such property, the
value of such property shall be determined by a panel of three appraisers whose
decision shall be final and binding on the parties hereto. The Transferring
Party shall choose one appraiser; the Company and/or the Non-Transferring
Parties acquiring such Shares Proposed for Transfer shall choose the second
appraiser; and the two so selected shall select and designate a third appraiser.
The value of the property shall be equal to the average of the values determined
by the three appraisers.

                  (g) Notwithstanding anything to the contrary herein, neither
the Company nor any of the Non-Transferring Parties shall have any right to
purchase any of the Shares Proposed for Transfer hereunder unless the Company
and/or the Non-Transferring Parties exercise their option or options to purchase
all of the Shares Proposed for Transfer.

                  (h) Notwithstanding anything to the contrary set forth herein,
in the event the Stockholder proposing to transfer its shares is an
Institutional Stockholder, the Company's right to purchase any or all of the
Shares Proposed for Transfer shall be conditioned upon the receipt by the
proposed selling Stockholder of either a satisfactory ruling from the relevant
taxing authority or a satisfactory option of legal counsel by such Stockholder
to the effect that the tax treatment of the proceeds on the sale of the Shares
Proposed for Transfer is not materially more adverse to the Stockholder if such
shares of Stock are purchased by the Company than would be the case if such
shares of Stock were purchased by the Offerer.

         3.6 SALE TO OFFERER; CLOSING. If the Company and/or the
Non-Transferring Parties do not exercise their options to purchase all of the
Shares Proposed for Transfer within the periods described in this Agreement (the
"Option Period"), then all options of the Company and the Non-Transferring
Parties to purchase such Shares Proposed for Transfer, whether exercised or not,
shall terminate and, subject to the provisions in Section 3.1, the Transferring
Party may sell, on the terms and conditions set forth in the Notice, the Shares
Proposed for Transfer to the Offerer,


                                      7.

<PAGE>

PROVIDED that the transaction contemplated by the Notice shall be consummated
not later than ninety (90) days after the expiration of the Option Period.

         3.7 CO-SALE RIGHTS. Upon the proposed occurrence of a Co-Sale
Transaction, any one or more of the Stockholders may demand that the
effectiveness of the Co-Sale Transaction be conditioned upon the right of such
Stockholder(s) to sell to the Person acquiring shares of Stock or other
securities of the Company (the "Co-Sale Purchaser") all or any part of such
Stockholder(s)' shares of Stock and other securities of the Company (a
"Co-Sale"), PROVIDED that such Stockholder(s) deliver(s) written notice to the
Stockholder transferring shares of Stock or other Company securities to the
Co-Sale Purchaser of such demand stating the number and kind of shares of Stock
and other securities it so wishes to sell within forty-five (45) days after
having received notice from the Transferring Party that a proposed sale of
shares of Stock would constitute a Co-Sale Transaction. The price for such
Stockholder(s)' shares of Stock and other securities of the Company shall be
equal to the per share price to be paid in the Co-Sale Transaction PROVIDED,
HOWEVER, that any such Stockholder and/or Transferring Party may demand that
proceeds from the Co-Sale Transaction be reallocated among such Stockholders and
the Transferring Party such that such Stockholders and the Transferring Party
shall be entitled to receive such portion of the proceeds as if the proceeds
were distributed pursuant to Section C.2.a. of Article IV of the Certificate and
PROVIDED FURTHER that such Stockholders and/or Transferring Party who tenders
securities which represent the right to purchase shares shall be entitled to
receive as consideration therefor the value of such shares (determined on the
basis of the terms and conditions applicable to the Co-Sale Transaction taking
into account the reallocation of the purchase price as aforesaid) purchasable on
the basis thereof less the exercise price, if any, of the applicable security.
The closing of the Co-Sale shall take place concurrently with the sale by the
Transferring Party to the Co-Sale Purchaser. If the Co-Sale Purchaser is
unwilling or unable to purchase all of the shares of Stock and other securities
such Stockholder(s) desire(s) to sell, neither the Company nor any Stockholder,
including the Transferring Party, shall enter into the Co-Sale Transaction. The
occurrence of a Co-Sale Transaction other than in connection with the purchase
of all of such Stockholder(s) tendered shares of Stock and other securities
shall be an Event of Default under this Agreement.

         3.8 TREATMENT OF SALE PROCEEDS. The proceeds of any sale made by any
Transferring Party without compliance with the provisions of this Article 3
shall be deemed to be held in constructive trust in such amount as would have
been due to the Stockholders desiring to sell shares of Stock or other
securities if the Transferring Party had complied with this Agreement.

                                    ARTICLE 4

                             COME-ALONG OBLIGATIONS

         4.1 GENERALLY. Each of the Stockholders (the "Participating
Sellers") hereby agrees, if requested by a Significant Number of Stockholders
(the Stockholders constituting such Significant Number of Stockholders are
hereinafter referred to as the "Come-Along Stockholders"), to sell all of his
or her shares of Stock and other securities of the Company to any other
Person (the "Proposed Buyer") in the manner and on the terms set forth in
this Article 4 in connection with the sale by the Come-Along Stockholders to
the Proposed Buyer of all of

                                     8.

<PAGE>

the shares and other securities of the Company of the Come-Along
Stockholders. Notwithstanding the foregoing, the provisions of this Article 4
shall not apply if the Proposed Buyer is an Affiliate of any Stockholder
which comprises a part of the Come-Along Stockholders.

         4.2 NOTICE. A "Come-Along Notice" shall be delivered by a Stockholder
which is a part of the Come-Along Stockholders on behalf of all such
Stockholders to the Participating Sellers. The Come-Along Notice shall set forth
the principal terms of the proposed purchase (the "Come-Along Transaction")
insofar as it relates to the shares of Stock and other securities of the
Company, the purchase price, the name and address of the Proposed Buyer and the
other principal terms of the proposed Come-Along Transaction. The price for such
Participating Sellers' shares of Stock and other securities of the Company shall
be equal to the per share price applicable to the Come-Along Transaction,
PROVIDED, HOWEVER, that any Stockholder may demand that the proceeds from the
Come-Along Transaction be reallocated among the Stockholders such that the
Stockholders shall be entitled to receive such portion of the proceeds as if the
proceeds were distributed pursuant to Section C.2.a. of Article IV of the
Certificate and PROVIDED FURTHER that such Stockholders who tender securities
which represent the right to purchase shares shall be entitled to receive as
consideration therefor the value of such shares (determined on the basis of the
terms and conditions applicable to the Come-Along Transaction taking into
account the reallocation of the purchase price as aforesaid) purchasable on the
exercise thereof less the exercise price, if any, of the applicable security.

         4.3 CLOSING.

                  (a) If the Come-Along Stockholders consummate the Come-Along
Transaction, the Participating Sellers shall be bound and obligated to sell all
of their shares of Stock and other securities of the Company in the Come-Along
Transaction on the same terms and conditions as the Come-Along Stockholders sell
their shares of Stock and other securities of the Company (including, without
limitation, an agreement to be liable, on a pro rata basis in accordance with
the proceeds received, in respect of any representations, warranties and
indemnities reasonably given in the Come-Along Transaction by the Come-Along
Stockholders). The Stockholders agree that they will also take such actions and
execute such documents and instruments as shall be necessary or desirable in
order to consummate the Come-Along Transaction expeditiously. If at the end of
the one hundred eightieth (180th) day following the date of the Come-Along
Notice the Come-Along Transaction has not been completed, the Come-Along
Stockholders shall be released from their obligations under the Come-Along
Notice, the Come-Along Notice shall be null and void, and it shall be necessary
for a separate Come-Along Notice to have been furnished and the terms and
provisions of this Article 4 separately complied with, in order to consummate a
Come-Along Transaction pursuant to this Article 4. All costs and expenses
incurred by the Come-Along Stockholders in connection with any proposed
Come-Along Transaction as to which a Come-Along Notice shall have been properly
given (whether or not consummated), including without limitation all attorneys'
fees and disbursements, all accounting fees and disbursements and all finders'
or brokerage fees or commissions, shall be paid by the Company.

                  (b) Notwithstanding any other provision of this Agreement, in
the event the consideration to be paid in exchange for shares of Stock and other
securities of the Company in


                                      9.

<PAGE>

the proposed Come-Along Transaction includes any securities and the receipt
thereof by a Participating Seller would require under applicable law (i) the
registration or qualification of such securities or of any person as a broker
or dealer or agent with respect to such securities or (ii) the provision to
any participant in the Come-Along Transaction of any information other than
such information as would be required under Regulation D promulgated under
the Securities Act in an offering made pursuant to said Regulation D solely
to "accredited investors" as defined in said Regulation D, the Stockholders
comprising the Come-Along Stockholders shall have no obligation to cause such
Participating Seller to receive as to each share and other securities of the
Company the same amount and kind of securities as the Come-Along Stockholders
to the extent of such receipt of securities, unless the Come-Along
Stockholders shall have elected to cause such requirements to have been
complied with to the extent necessary to permit such Participating Seller to
receive such securities. The Participating Seller shall be entitled to
receive, in lieu thereof, against surrender of the shares and other
securities of the Company (in accordance with the last paragraph of this
Section 4.3 which would have otherwise been transferred by such Participating
Seller to the Proposed Buyer in the Come-Along Transaction, an amount in cash
equal to the fair market value of the securities which such Participating
Seller would otherwise have received (as determined in good faith by the
Board of Directors in its sole discretion). In the event such requirements
have been complied with to the extent necessary to permit such Participating
Seller to receive such securities, the Participating Seller shall execute
such documents and instruments, and take such other actions (including
without limitation, if required by the Come-Along Stockholders, agreeing to
be represented, without cost to the Participating Seller, during the course
of such Come-Along Transaction by a "purchaser representative" (as defined in
Regulation D) in connection with evaluating the merits and risks of the
prospective investment and acknowledging that he was so represented), as the
Proposed Buyer or the Company shall reasonably request in order to permit
such requirements to have been complied with; PROVIDED, HOWEVER, that such
actions shall not include any expenditure of funds by the Participating
Seller, it being understood that payment by the Participating Seller of the
fees and disbursements of any counsel the Participating Seller may elect to
retain shall be deemed not to constitute a required expenditure of funds for
purposes of this provision.

                  (c) At the closing of any Come-Along Transaction under this
Article 4, the Participating Sellers shall deliver the shares of Stock and other
securities of the Company to be sold by them, duly endorsed for transfer with
signature guaranteed, free and clear of any liens, against delivery of the
applicable purchase price.

         4.4 STOCK OPTIONS. The parties agree that in connection with the
Company's issuance of stock options pursuant to its 1997 Stock Option Plan the
Company shall impose, to the extent permissible by law, obligations similar to
the provisions in Sections 4.1, 4.2 and 4.3 on the holders of such stock
options.

                                    ARTICLE 5

                                EVENTS OF DEFAULT

         5.1 EVENTS OF DEFAULT. The following events shall be Events of Default
under this Agreement:


                                     10.

<PAGE>

                  (a) The Company shall fail to perform or comply in any
material respect with any of its covenants and agreements in this Agreement, or
under the Certificate or By-Laws and the failure has not been cured within the
Cure Period (a "Company Default").

                  (b) Any Stockholder shall fail to perform or comply in any
material respect with any of its covenants and agreements in this Agreement, and
the failure has not been cured within the Cure Period (a "Stockholder Default").

         5.2 REMEDIES ON DEFAULT. Upon the occurrence of a Company Default or a
Stockholder Default, notice of default shall promptly be given to the defaulting
party. The defaulting party shall have a period of thirty (30) days from the
date of receipt of such notice (the "Cure Period") in which to cure such
default, which it shall in good faith attempt to do. If the Event of Default
shall be continuing at the end of the Cure Period, the non-defaulting parties
shall have available to them all remedies that may be available to them in law
or in equity. In addition, if the default is a Company Default or a Stockholder
Default by the Founding Stockholder, then upon request by any Stockholder not in
default, such Stockholders not in default shall be entitled to appoint to the
Board of Directors that number of directors as shall enable directors appointed
by such Stockholders not in default to approve a Significant Action. Each
Stockholder agrees that it will take any action necessary (including but not
limited to the grant of proxies or the voting of shares of Stock) requested of
it to effect the intention of this provision.

         5.3 NOTICE OF DEFAULT. When any Event of Default shall have occurred,
the Company shall give written notice thereof to each Stockholder within 5
business days after the date that is the earlier of (i) the date that the
Company knows of, or (ii) the date that the Company receives written notice of,
such Event of Default. When in the judgment of any Stockholder an Event of
Default has occurred, the Stockholder shall give written notice thereof to the
Company PROVIDED that the failure to give such notice shall not be a waiver of
the rights of the Stockholder.

         5.4 SPECIFIC ENFORCEMENT. The parties hereto agree that a remedy at law
would not be adequate if a Company Default or a Stockholder Default by the
Founding Stockholder shall have occurred and be continuing. Unless such Default
shall have been waived, the Stockholders not in default may proceed to enforce
their rights under this Article 5 by a suit in equity or an action at law,
including without limitation, a suit for specific performance or injunctive
relief. It is agreed that if one or more Stockholder(s) not in default prevail
in such an action, such prevailing Stockholder(s) shall be entitled to receive
from the Company all reasonable fees, costs and expenses incurred by it,
including without limitation, reasonable fees and expenses of counsel.

         5.5 REMEDIES NOT WAIVED. No course of dealing between the Company and
any Stockholder and no delay in exercising any right, power or remedy conferred
hereunder, shall operate as a waiver of such right, power or remedy or otherwise
prejudice the exercise thereof.


                                      11.

<PAGE>

                                   ARTICLE 6

                                   GOVERNANCE

         6.1 COMPOSITION OF THE BOARD.

                  (a) Each Stockholder agrees to take any and all action
necessary (including, without limitation, the voting of all shares of Stock
owned or held by such Stockholder or over which such Stockholder has voting
control, the execution and delivery of proxies and actions in writing, and the
calling or joining in the calling of special stockholder meetings) to cause
eight Stockholder designees to be elected to the Board of Directors as follows:
(i) one member designated by BankInvest ("BI"), (ii) one member designated by
Dansk Kapitalanlaeg Aktieselskab ("DK"), (iii) one member jointly designated by
Lonmodtagernes Dyrtidsfond ("LD") and Kommunernes Pensionsforsikring A/S ("KP"),
(iv) one member designated by ABN AMRO Ventures B.V., (v) one member designated
by the holders of a majority of the Series E Preferred Stock and (vi) three
members designated by the Founding Stockholder (PROVIDED that one of the
Founding Stockholder's designees shall be the Chief Executive Officer of the
Company).

                  (b) The Stockholders acknowledge that pursuant to Article IV,
Section C.3.e of the Certificate, the holders of the Company's Series C
Preferred Stock are entitled to elect one director in addition to the directors
elected pursuant to Section 6.1(a) of this Agreement.

                  (c) Any director who is elected to the Board of Directors
pursuant to a designation under Section 6.1(a) above may be removed from the
Board of Directors during or upon the completion of such director's term by (and
only by) the Stockholder having made the designation. Upon the occurrence of a
vacancy in the Board of Directors occasioned by the resignation, retirement,
death, disability or removal, or the expiration of the term, of a director
designated under Section 6.1(a) above, the Stockholder having designated such
director shall be entitled to designate the successor thereto and the name of
the individual so designated shall be promptly submitted to the Stockholders for
election by the most expeditious means practicable, and the Stockholders agree
to cause the election of such new designee.

                  (d) The Board of Directors shall elect, from among the
directors of the Company, other than directors designated by the Founding
Stockholder, a chairman of the Board of Directors (the "Chairman"). The Chairman
shall chair all meetings of the Board of Directors and have any other duties
assigned to him by the Board of Directors.

                  (e) The parties agree that given the nature of the Major
Institutional Stockholders, to the extent permitted by applicable law, any
directors appointed pursuant to Section 6.1(a)(i), (ii), (iii), (iv) or (v)
above shall not have a duty to offer to the Company business opportunities of
which such director becomes aware and which falls within the scope of the
business conducted by the Stockholder by whom such director was designated.

                  (f) Any director appointed pursuant to Section 6.1(a)(i),
(ii), (iii), (iv) or (v) will be entitled to indemnification to the full extent
provided by the Certificate and the Corporation law.


                                     12.

<PAGE>

         6.2 FREQUENCY, QUORUM AND VOTING. Regular meetings of the Board of
Directors shall take place no less than four (4) times per year, I.E. one
regular meeting in each calendar quarter. Unless otherwise agreed by all
directors, at least two (2) board meetings per year shall be held in Denmark and
at least two (2) board meetings per year shall be held in the United States.

         6.3 NOTICE OF MEETINGS. The Company shall provide all directors and any
Board Observer with not less than thirty (30) days' notice of all regular
meetings of the Board of Directors, and shall provide such directors with a
detailed agenda of the items to be discussed at such meeting (PROVIDED that a
revised agenda and related materials may be provided to such persons less than
30 days before the meeting). Compliance with such notice provision may be waived
in writing by a director. Any waiver shall be applicable only to one meeting of
the Board of Directors.


         6.4 SPECIAL MEETINGS. Special meetings of the Board of Directors may be
called, on not less than eight (8) days' notice by not fewer than two directors,
at least one of whom shall have been appointed pursuant to Sections 6.1(a)(i),
(ii), (iii), (iv) or (v) and at least one of whom shall have been appointed
pursuant to Section 6.1(a)(vi). The Chairman shall use all reasonable efforts to
communicate in advance of any special meeting with directors who are unable to
attend such meeting to elicit their views on actions proposed to be taken at the
special meeting. Compliance with the notice provision in this paragraph may be
waived in writing by a director. Any waiver shall be applicable only to one
meeting of the Board of Directors.

         6.5 COMPOSITION OF COMMITTEES. Every committee of the Board of
Directors shall include at least one director designated pursuant to Sections
6.1(a)(i), (ii), (iii), (iv) or (v).

         6.6 GOVERNANCE OF SUBSIDIARIES. The Stockholders agree that the board
of directors of each subsidiary of the Company shall be appointed to reasonably
reflect the interests of the Stockholders. Any Major Stockholder may require
that the board of directors of any subsidiary of the Company be comprised of a
number of directors equal to the number of directors of the Company. In such
event, the directors of such subsidiary shall be appointed in the manner
provided herein with respect to the designation of the Board of Directors.

         6.7 STOCKHOLDERS' OBLIGATIONS TO TAKE CERTAIN ACTIONS. Each Stockholder
covenants and agrees that to the extent the effectuation of any Significant
Action requires any act of any Stockholder, such Stockholder will take any
action requested of it by the Board of Directors (including the execution of
proxies, consents, documents or certificates) necessary or helpful to effect the
Significant Action that has been approved as provided for herein.

         6.8 LIMITATION ON DIRECTORS' ACTIONS. Without the consent of all of the
directors who have no interest in any transaction proposed between the Company
and a director or a Stockholder, no director who has an interest in any such
transaction and no director who is a designee of a Stockholder who has an
interest in such a transaction, shall vote upon such transaction. For purposes
of this Section 6.8, the term "transaction" shall not include the decision to
employ or to terminate the employment of an individual, except where the
termination is for cause as defined in the relevant employment agreement, if
any.


                                      13.

<PAGE>

                                    ARTICLE 7

                      AFFIRMATIVE COVENANTS OF THE COMPANY

         The Company hereby covenants and agrees with the Institutional
Stockholders as follows:

         7.1 MATERIAL CHANGES AND LITIGATION. The Company shall promptly notify
the Major Institutional Stockholders of any material adverse change in the
business, assets or condition, financial or otherwise, of the Company, of any
defaults by the Company under any material contract(s) to which the Company is a
party, and of any litigation or governmental proceeding or investigation brought
or, to the best of the Company's knowledge, threatened against the Company, the
Founding Stockholder, any officer, director, key employee or principal
stockholder of the Company which, if adversely determined, would materially
adversely affect the Company or its business, prospects, assets or condition,
financial or otherwise.

         7.2 TRANSACTIONS WITH AFFILIATES. The Company shall promptly disclose
to the Institutional Stockholders the existence of any transaction or
arrangement of which the Company has knowledge with or for the benefit of a
Stockholder, officer or director of the Company or any Affiliate or a member of
the immediate family of the foregoing. In addition, the Company shall require
the prompt disclosure to the Company of any arrangement or transaction involving
any such person. The Company shall not knowingly enter into an arrangement or
transaction with any such person except in conformity with Article 8 hereof.

         7.3 BOARD OBSERVER. The Company will permit any Stockholder who owns at
least five hundred thousand (500,000) shares of capital stock in the Company,
taking into account shares of Preferred Stock issuable upon declaration of the
Special Dividend, to appoint one observer to the Board of Directors (a "Board
Observer"). The Board Observer shall be entitled to attend all meetings of the
Board of Directors and to receive such notice and other information with respect
to such meetings as are delivered to the directors of the Company. The Company
shall not be obligated to reimburse the expenses incurred by the Board Observer.

         7.4 CORPORATE EXISTENCE. The Company shall maintain at all times its
existence as a corporation incorporated and in good standing under the laws of
the State of Delaware, and shall file all necessary documentation, tax returns,
reports and related information required to maintain such existence.

         7.5      FINANCIAL STATEMENTS AND OTHER INFORMATION.

                  (a) The Company shall deliver to each Institutional
Stockholder:

                           (i) within 120 days after the end of each fiscal year
of the Company, an audited balance sheet of the Company as at the end of such
year and audited statements of operations and of cash flows of the Company for
such year, certified by a "Big Five" certified public accountant firm selected
by the Company, and prepared in accordance with generally accepted accounting
principles; and

                           (ii) within 45 days after the end of each fiscal
quarter of the Company, an unaudited balance sheet of the Company as at the end
of such quarter, and unaudited


                                     14.

<PAGE>

statements of operations and of cash flows of the Company for such fiscal
quarter and for the current fiscal year to the end of such fiscal quarter.

                  (b) The Company shall deliver to each Major Institutional
Stockholder:

                           (i) within 30 days after the end of each month, an
unaudited balance sheet of the Company as at the end of such month and unaudited
statements of income and of cash flows of the Company for such month and for the
current fiscal year to the end of such month, setting forth in comparative form
the Company's projected financial statement for the corresponding periods for
the current fiscal year;

                           (ii) as soon as available, but in any event within 30
days before commencement of each new fiscal year, a three-year rolling business
plan and a budget (including a capital expenditures budget) for the new fiscal
year.

                           (iii) with reasonable promptness, such other notices,
information and data with respect to the Company as the Company delivers to the
holders of its Common Stock, and such other information and data as such Major
Institutional Stockholder may from time to time reasonably request.

                  (c) Financial statements shall be prepared on a consolidated
basis if the Company then has any majority-owned subsidiaries. The financial
statements delivered pursuant to clause (ii) of paragraph (a) and clause (i) of
paragraph (b) shall be accompanied by a certificate of the chief financial
officer of the Company stating that such statements have been prepared in
accordance with generally accepted accounting principles consistently applied
(except as noted) and fairly present the financial condition and results of
operations of the Company at the date thereof and for the periods covered
thereby.

         7.6 INSPECTION OF BOOKS AND RECORDS. The Company shall permit each
Stockholder holding more than five hundred thousand (500,000) shares of capital
stock, taking into account shares of Preferred Stock issuable upon declaration
of the Special Dividend, or any authorized representative thereof, to visit and
inspect the properties of the Company, including corporate and financial
records, and to discuss its business and finances with officers of the Company,
during normal business hours following reasonable notice and as often as may be
reasonably requested, PROVIDED that such Stockholder executes and delivers a
confidentiality agreement in form and substance reasonably satisfactory to the
Company prior to any such visit and inspection.

         7.7 PAYMENT OF TAXES. The Company shall pay all income, franchise, real
property, sales and other taxes, assessments and levies (whether federal, state
or local) promptly when due.

         7.8 INSURANCE. Until February 3, 2002, the Company shall maintain term
life insurance upon the life of Mark R. Brann in the amount of Five Million
United States Dollars (US $5,000,000), with the proceeds payable to the Company.

         7.9 PATENTS AND INTELLECTUAL PROPERTY. The Company shall maintain a
policy governing the development, use, licensing and protection of its patents
and intellectual property.


                                      15.

<PAGE>


         7.10 NONDISCLOSURE AGREEMENTS. The Company shall require all persons
now or hereafter employed by the Company, whether as employees or consultants,
and who have access to confidential and proprietary information of the Company
to enter into nondisclosure and assignment of inventions agreements in such form
as may be approved by the Board of Directors.

         7.11 EXPENSES AND COMPENSATION OF DIRECTORS.

                  (a) The Company shall promptly reimburse in full each director
of the Company for all reasonable out-of-pocket expenses incurred in attending
each meeting of the Board of Directors or any committee thereof, including,
without limitation, reasonable travel and lodging expenses.

                  (b) The Company shall pay to members of the Board of Directors
who are not employees of the Company annual compensation for their services
pursuant to a compensation arrangement approved by the Board of Directors.

         7.12 RESERVATION OF COMMON STOCK. The Company shall reserve and
maintain a sufficient number of shares of Common Stock for issuance pursuant to
its obligations set forth in the Certificate, and/or issuable upon the exercise
of the Warrants.

         7.13 INTERNATIONAL INVESTMENT AND TRADE IN SERVICES SURVEY ACT. The
Company shall use its best efforts to file on a timely basis all reports
required to be filed by it under 22 U.S.C Section 3104, or any similar statute,
relating to a foreign person's direct or indirect investment in the Company.

         7.14 COPENHAGEN LEAD DISCOVERY PROJECT. The Company agrees to use its
best efforts to develop the Copenhagen Project and to fully utilize proceeds of
the Loan Commitment for that purpose.

         7.15 NOTICE OF CERTAIN BREACHES. The Company covenants and agrees that
it will promptly (but in any event within five (5) business days from the
Company becoming aware of such event) notify the Institutional Stockholders of
any event which alone or with the passage of time or the giving of notice would
constitute a breach of any representation or warranty made by the Company or the
Founding Stockholder in the Series E Stock Purchase Agreement.

         7.16 BUDGETS. The Company agrees that at least 30 days prior to the
commencement of each fiscal year it shall submit to its Board of Directors a
budget for the ensuing fiscal year.

         7.17 CONDUCT OF BUSINESS. The Company covenants and agrees with the
Institutional Investors that it shall, and shall require its officers and
employees to, conduct the business of the Company in accordance with the
business plan and budget approved by the Board of Directors, and otherwise in
accordance with applicable law, rules and regulations and with the highest
professional and ethical standards.

         7.18 PRESERVATION OF SHARES. The Company shall at all times when the
Preferred Stock shall be outstanding, reserve and keep available out of its
authorized but unissued Preferred Stock, for the purpose of declaring and
issuing a Special Dividend, such number of its


                                     16.

<PAGE>

duly authorized shares of Preferred Stock as shall from time to time be
sufficient to declare and issue the Special Dividend in accordance with the
Certificate.

                                    ARTICLE 8

                               NEGATIVE COVENANTS

         The Company shall not take any Significant Action without the prior
approval of the Specified Majority of the Board of Directors. Notwithstanding
the foregoing, the prior approval of the Specified Majority of Directors shall
not be required for the Company to pay the expenses incurred by it in connection
with the transactions contemplated by the Series E Stock Purchase Agreement.

                                    ARTICLE 9

                               REGISTRATION RIGHTS

         9.1 REQUIRED REGISTRATIONS.

                  (a) At any time after the earlier of January 15, 2001 or the
Company's Initial Public Offering, an Institutional Stockholder or Stockholders
holding in the aggregate at least 40% of the Registrable Shares may request, in
writing, that the Company effect the registration on Form S-1 or Form S-2 (or
any successor form) of the Registrable Shares owned by such Institutional
Stockholder or Stockholders having an aggregate offering price of at least
$7,500,000 (based on the then current market price or fair value). If the
holders initiating the registration intend to distribute the Registrable Shares
by means of an underwriting, they shall so advise the Company in their request.
In the event such registration is underwritten, the right of other Institutional
Stockholders to participate shall be conditioned on such Stockholders'
participation in such underwriting. Upon receipt of any such request, the
Company shall promptly give written notice of such proposed registration to all
Institutional Stockholders. Such Stockholder shall have the right, by giving
written notice to the Company within 30 days after the Company provides its
notice, to elect to have included in such registration such of their Registrable
Shares as such Institutional Stockholders may request in such notice of
election; PROVIDED that if the underwriter (if any) managing the offering
determines that, because of marketing factors, all of the Registrable Shares
requested to be registered by all Institutional Stockholders may not be included
in the offering, then all Institutional Stockholders who have requested
registration shall participate in the registration pro rata based upon the
number of Registrable Shares which they have requested to be so registered. If
the underwriter has not limited the number of Registrable Shares to be
underwritten, the Company may include securities for its own account (or for the
account of other stockholders) in such registration if the underwriter so agrees
and if the number of Registrable Shares that would otherwise have been included
in such registration and underwriting will not thereby be limited. Thereupon,
the Company shall, as expeditiously as possible, use its best efforts to effect
the registration on Form S-1 or Form S-2 (or any successor form) of all
Registrable Shares which the Company has been requested to so register.


                                     17.
<PAGE>

                  (b) At any time after the Company becomes eligible to file a
Registration Statement on Form S-3 (or any successor form relating to secondary
offerings), an Institutional Stockholder or Stockholders holding in the
aggregate at least 25% of the Registrable Shares may request the Company, in
writing, to effect the registration on Form S-3 (or such successor form), of
Registrable Shares having an aggregate offering price of at least $500,000
(based on the then current public market price). Upon receipt of any such
request, the Company shall promptly give written notice of such proposed
registration to all the Institutional Stockholders. Such stockholders shall have
the right, by giving written notice to the Company within 30 days after the
Company provides its notice, to elect to have included in such registration such
of their Registrable Shares as such Institutional Stockholders may request in
such notice of election; PROVIDED that if the underwriter (if any) managing the
offering determines that, because of marketing factors, all of the Registrable
Shares requested to be registered by all Institutional Stockholders may not be
included in the offering, then all such Stockholders who have requested
registration shall participate in the registration pro rata based upon the
number of Registrable Shares which they have requested to be so registered. If
the underwriter has not limited the number of Registrable Shares to be
underwritten, the Company may include securities for its own account (or for the
account of other stockholders) in such registration if the underwriter so agrees
and if the number of Registrable Shares that would otherwise have been included
in such registration and underwriting will not thereby be limited. Thereupon,
the Company shall, as expeditiously as possible, use its best efforts to effect
the registration on Form S-3 (or such successor form) of all Registrable Shares
which the Company has been requested to so register.

                  (c) The Company shall not be required to effect more than two
registrations pursuant to paragraph (a) above or more than three registrations
pursuant to paragraph (b) above. In addition, the Company shall not be required
to effect any registration (other than on Form S-3 or any successor form
relating to secondary offerings) within six months after the effective date of
any other Registration Statement of the Company.

                  (d) If at the time of any request to register Registrable
Shares pursuant to this Section 9.1, the Company is engaged or has fixed plans
to engage within 30 days of the time of the request in a registered public
offering as to which the Institutional Stockholders may include Registrable
Shares pursuant to Section 9.2 or is engaged in any other activity which, in the
good faith determination of the Board of Directors, would be adversely affected
by the requested registration to the material detriment of the Company, then the
Company may at its option direct that such request be delayed for a period not
in excess of six months from the effective date of such offering or the date of
commencement of such other material activity, as the case may be, such right to
delay a request may not be exercised by the Company more than once in any
two-year period.

         9.2 INCIDENTAL REGISTRATION.

                  (a) Whenever the Company proposes to file a Registration
Statement (other than pursuant to Section 9.1) at any time and from time to
time, it will, prior to such filing, give written notice to all Institutional
Stockholders of its intention to do so and, upon the written request of an
Institutional Stockholder or Stockholders given within 20 days after the Company
provides such notice (which request shall state the intended method of
disposition of such Registrable Shares), the Company shall use its best efforts
to cause all Registrable Shares which


                                      18.

<PAGE>

the Company has been requested by such Institutional Stockholder or
Stockholders to register to be registered under the Securities Act to the
extent necessary to permit their sale or other disposition in accordance with
the intended methods of distribution specified in the request of such
Institutional Stockholder or Stockholders; PROVIDED that the Company shall
have the right to postpone or withdraw any registration effected pursuant to
this Section 9.2 without obligation to any Stockholder.

                  (b) In connection with any registration under this Section 9.2
involving an underwriting, the Company shall not be required to include any
Registrable Shares in such registration unless the holders thereof accept the
terms of the underwriting as agreed upon between the Company and the
underwriters selected by it (PROVIDED that such terms must be consistent with
this Agreement). If in the opinion of the managing underwriter it is appropriate
because of marketing factors to limit the number of Registrable Shares to be
included in the offering, then the Company shall be required to include in the
registration only that number of Registrable Shares, if any, which the managing
underwriter believes should be included therein; PROVIDED that no persons or
entities other than the Company, the Institutional Stockholders and persons or
entities holding registration rights shall be permitted to include securities in
the offering. If the number of Registrable Shares to be included in the offering
in accordance with the foregoing is less than the total number of shares which
the holders of Registrable Shares have requested to be included, then the
holders of Registrable Shares who have requested registration and other holders
of securities entitled to include them in such registration shall participate in
the registration pro rata based on their total ownership of shares of Common
Stock (giving effect to the conversion into Common Stock of all securities
convertible thereinto).

         9.3 REGISTRATION PROCEDURES. If and whenever the Company is required by
the provisions of this Agreement to use its best efforts to effect the
registration of any of the Registrable Shares under the Securities Act, the
Company shall:

                  (a) promptly file with the Commission a Registration Statement
with respect to such Registrable Shares and use its best efforts to cause that
Registration Statement to become effective;

                  (b) as expeditiously as possible prepare and file with the
Commission any amendments and supplements to the Registration Statement and the
prospectus included in the Registration Statement as may be necessary to keep
the Registration Statement effective, in the case of a firm commitment
underwritten public offering, until each underwriter has completed the
distribution of all securities purchased by it and, in the case of any other
offering, until the earlier of the sale of all Registrable Shares covered
thereby or 120 days after the effective date thereof;

                  (c) as expeditiously as possible furnish to each selling
Institutional Stockholder such reasonable numbers of copies of the prospectus
and the Registration Statement, including a preliminary prospectus, in
conformity with the requirements of the Securities Act, and such other documents
as the selling Institutional Stockholder may reasonably request in order to
facilitate the public sale or other disposition of the Registrable Shares owned
by the selling Institutional Stockholder;


                                     19.

<PAGE>

                  (d) as expeditiously as possible use its best efforts to
register or qualify the Registrable Shares covered by the Registration Statement
under the securities or Blue Sky laws of such states as the selling
Institutional Stockholders shall reasonably request, and do any and all other
acts and things that may be necessary or desirable to enable the selling
Institutional Stockholders to consummate the public sale or other disposition in
such states of the Registrable Shares owned by the selling Institutional
Stockholder; PROVIDED, HOWEVER, that the Company shall not be required in
connection with this paragraph (d) to qualify as a foreign corporation or
execute a general consent to service of process in any jurisdiction; and

                  (e) furnish to each prospective selling Institutional
Stockholder a signed counterpart of (i) an opinion of counsel for the Company
delivered to the underwriters, dated the effective date of the Registration
Statement, and (ii) to selling Institutional Stockholders from the independent
auditors of the Company, a "comfort" letter delivered to the underwriters and
signed by the independent auditors who have certified the Company's financial
statements included in the Registration Statement, covering substantially the
same matter with respect to events subsequent to the date of the financial
statements, as are customarily covered (at the time of such registration) in
opinions of issuer's counsel and in "comfort" letters delivered to the
underwriters in underwritten public offerings of securities.

         If the Company has delivered preliminary or final prospectuses to the
selling Institutional Stockholders and after having done so the prospectus is
amended to comply with the requirements of the Securities Act, the Company shall
promptly notify the selling Institutional Stockholders and, if requested, the
selling Institutional Stockholders shall immediately cease making offers of
Registrable Shares and return all prospectuses to the Company. The Company shall
promptly provide the selling Institutional Stockholders with revised
prospectuses and, following receipt of the revised prospectuses, the selling
Institutional Stockholders shall be free to resume making offers of the
Registrable Shares.

         9.4 ALLOCATION OF EXPENSES. The Company will pay all Registration
Expenses of all registrations under this Agreement; PROVIDED, HOWEVER, that if a
registration under Section 9.1 is withdrawn at the request of the Institutional
Stockholders requesting such registration (other than as a result of information
concerning the business or financial condition of the Company which is made
known to the Institutional Stockholders after the date on which such
registration was requested) and if the requesting Institutional Stockholders
elect, by majority vote of the securities registered for such Institutional
Stockholders, not to have such registration counted as a registration requested
under Section 9.1, the requesting Institutional Stockholders shall pay the
Registration Expenses of such registration pro rata in accordance with the
number of their Registrable Shares included in such registration. For purposes
of this Section 9.4, the term "Registration Expenses" shall mean all expenses
reasonably incurred by the Company in complying with this Agreement, including,
without limitation, all registration and filing fees, exchange listing fees,
printing expenses, fees and expenses of counsel for the Company and the fees and
expenses of one counsel selected by the selling Institutional Stockholders to
represent the selling Institutional Stockholders, state Blue Sky fees and
expenses, and the expense of any special audits incident to or required by any
such registration, but excluding underwriting discounts, selling commissions and
the fees and expenses of selling Institutional Stockholders' own counsel (other
than the counsel selected to represent all selling Institutional Stockholders).


                                     20.

<PAGE>

         9.5 INDEMNIFICATION AND CONTRIBUTION.

                  (a) In the event of any registration of any of the Registrable
Shares under the Securities Act pursuant to this Agreement, the Company will
indemnify and hold harmless the seller of such Registrable Shares, each
underwriter of such Registrable Shares, and each other person, if any, who
controls such seller or underwriter within the meaning of the Securities Act or
the Exchange Act against any losses, claims, damages or liabilities, joint or
several, to which such seller, underwriter or controlling person may become
subject under the Securities Act, the Exchange Act, state securities or Blue Sky
laws or otherwise, insofar as such losses, claims, damages or liabilities (or
actions in respect thereof) arise out of or are based upon any untrue statement
or alleged untrue statement of any material fact contained in any Registration
Statement under which such Registrable Shares were registered under the
Securities Act, any preliminary prospectus or final prospectus contained in the
Registration Statement, or any amendment or supplement to such Registration
Statement or arise out of or are based upon the omission or alleged omission to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading; and the Company will reimburse such seller,
underwriter and each such controlling person for any legal or any other expenses
reasonably incurred by such seller, underwriter or controlling person in
connection with investigating or defending any such loss, claim, damage,
liability or action; PROVIDED, HOWEVER, that the Company will not be liable in
any such case to the extent that any such loss, claim, damage or liability
arises out of or is based upon any untrue statement or omission made in such
Registration Statement, preliminary prospectus or final prospectus, or any such
amendment or supplement, in reliance upon and in conformity with information
furnished to the Company, in writing, by or on behalf of such seller,
underwriter or controlling person specifically for use in the preparation
thereof.

                  (b) In the event of any registration of any of the Registrable
Shares under the Securities Act pursuant to this Agreement, each seller of
Registrable Shares, severally and not jointly, will indemnify and hold harmless
the Company, each of its directors and officers and each underwriter (if any)
and each person, if any, who controls the Company or any such underwriter within
the meaning of the Securities Act or the Exchange Act, against any losses,
claims, damages or liabilities, joint or several, to which the Company, such
directors and officers, underwriter or controlling person may become subject
under the Securities Act, Exchange Act, state securities or Blue Sky laws or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) arise out of or are based upon any untrue statement or alleged
untrue statement of a material fact contained in any Registration Statement
under which such Registrable Shares were registered under the Securities Act,
any preliminary prospectus or final prospectus contained in the Registration
Statement, or any amendment or supplement to the Registration Statement, or
arise out of or are based upon any omission or alleged omission to state a
material fact required to be stated therein or necessary to make the statement
therein not misleading, if the statement or omission was made in reliance upon
and in conformity with information relating to such seller furnished in writing
to the Company by or on behalf of such seller specifically for use in connection
with the preparation of such Registration Statement, prospectuses, amendment or
supplement; PROVIDED, HOWEVER, that the obligations of such Institutional
Stockholders hereunder shall be limited to an amount equal to the proceeds to
each Institutional Stockholder of Registrable Shares sold in connection with
such registration.


                                     21.

<PAGE>

                  (c) Each party entitled to indemnification under this Section
9.5 (the "Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom; PROVIDED that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or litigation, shall be
approved by the Indemnified Party (whose approval shall not be unreasonably
withheld); and, PROVIDED FURTHER that the failure of any Indemnified Party to
give notice as provided herein shall not relieve the Indemnifying Party of its
obligations under this Section 9.5. The Indemnified Party may participate in
such defense at such party's expense; PROVIDED, HOWEVER, that the Indemnifying
Party shall pay such expense if representation of such Indemnified Party by the
counsel retained by the Indemnifying Party would be inappropriate due to actual
or potential differing interests between the Indemnified Party and any other
party represented by such counsel in such proceeding. No Indemnifying Party, in
the defense of any such claim or litigation shall, except with the consent of
each Indemnified Party, consent to entry of any judgment or enter into any
settlement which does not include as an unconditional term thereof the giving by
the claimant or plaintiff to each Indemnified Party of a release from all
liability in respect of such claim or litigation, and no Indemnified Party shall
consent to entry of any judgment or settle such claim or litigation without the
prior written consent of each other Indemnified Party.

                  (d) In order to provide for just and equitable contribution to
joint liability under the Securities Act in any case in which either (i) any
holder of Registrable Shares exercising rights under this Agreement, or any
controlling person of any such holder, makes a claim for indemnification
pursuant to this Section 9.5 but it is judicially determined (by the entry of a
final judgment or decree by a court of competent jurisdiction and the expiration
of time to appeal or the denial of the last right of appeal) that such
indemnification may not be enforced in such case notwithstanding the fact that
this Section 9.5 provides for indemnification in such case, or (ii) contribution
under the Securities Act may be required on the part of any such selling
Institutional Stockholder or any such controlling person in circumstances for
which indemnification is provided under this Section 9.5; then each Indemnifying
Party shall contribute to the amount paid or payable by such Indemnified Party
as a result of such losses, claims, liabilities, or expenses (or actions in
respect thereof) in such proportion as is appropriate to reflect the relative
fault of the Indemnifying Party and the Indemnified Party as well as any other
relevant equitable considerations. The relative fault of such Indemnifying Party
and Indemnified Party shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of a material fact or omission or
alleged omission to state a material fact relates to information supplied by
such Indemnifying Party or Indemnified Party, and the parties' relative
knowledge, access to information and opportunity to correct or prevent such
statement or omission. The parties hereto agree that it would not be just and
equitable if contribution pursuant to this Section 9.5(d) were determined by pro
rata allocation (even if the Holders were treated as one entity for such
purpose) or by any other method of allocation which does not take account of the
equitable considerations referred to in this Section 9.5(d). The amount paid or
payable by an Indemnified Party as result of the losses, claims, damages,
liabilities, or expenses (or actions in respect thereof) referred to above shall
be deemed to include any legal or other fees or expenses reasonably incurred by
such Indemnified Party in connection with investigating or, except as provided
in Section 9.5(c), defending any such action or claim. Notwithstanding the


                                      22.

<PAGE>

provisions of this Section 9.5(d), (A) no such holder will be required to
contribute any amount in excess of the proceeds to it of all Registrable Shares
sold by it pursuant to such Registration Statement, and (B) no person or entity
guilty of fraudulent misrepresentation, within the meaning of Section 11(f) of
the Securities Act, shall be entitled to contribution from any person or entity
who is not guilty of such fraudulent misrepresentations.

         9.6 INDEMNIFICATION WITH RESPECT TO UNDERWRITTEN OFFERING. In the event
that Registrable Shares are sold pursuant to a Registration Statement in an
underwritten offering pursuant to Section 9.1, the Company agrees to enter into
an underwriting agreement containing customary representations and warranties
with respect to the business and operations of an issuer of the securities being
registered and customary covenants and agreement to be performed by such issuer,
including without limitation customary provisions with respect to
indemnification by the Company of the underwriters of such offering.

         9.7 INFORMATION BY HOLDER. Each Institutional Stockholder including
Registrable Shares in any registration shall furnish to the Company such
information regarding such Institutional Stockholder and the distribution
proposed by such Institutional Stockholder as the Company may reasonably request
in writing and as shall be required in connection with any registration,
qualification or compliance referred to in this Agreement.

         9.8 "STAND-OFF" AGREEMENT. Each Institutional Stockholder, if requested
by the Company and the managing underwriter of an offering by the Company of
Common Stock or other securities of the Company pursuant to a Registration
Statement, shall agree not to sell publicly or otherwise transfer or dispose of
any Registrable Shares or other securities of the Company held by such
Institutional Stockholder for a specified period of time (not to exceed 180
days) following the effective date of such Registration Statement; PROVIDED
that:

                  (a) such agreement shall only apply to the first Registration
Statement covering Common Stock of the Company to the public in an underwritten
offering; and

                  (b) all Institutional Stockholders holding not less than the
number of shares of Common Stock held by such Institutional Stockholder
(including shares of Common Stock issuable upon the conversion of shares of
Stock, or other convertible securities, or upon the exercise of options,
warrants or rights) and all officers and directors of the Company enter into
similar agreements.

         9.9 RULE 144 REQUIREMENTS. After the effective date of the first
Registration Statement filed by the Company for an offering of its securities to
the public, the Company agrees to:

                  (a) make and keep public information available in compliance
with the requirements of Rule 144 under the Securities Act;

                  (b) use its best efforts to file with the Commission in a
timely manner all reports and other documents required of the Company under the
Securities Act and the Exchange Act; and


                                      23.

<PAGE>

                  (c) furnish to a holder of Registrable Shares upon request (i)
a written statement by the Company as to its compliance with the reporting
requirements of said Rule 144, and the reporting requirements of the Securities
Act and the Exchange Act, (ii) a copy of the most recent annual or quarterly
report of the Company, and (iii) such other reports and documents of the Company
as such holder may reasonably request to avail itself of any similar rule or
regulation of the Commission allowing it to sell any such securities without
registration.

         9.10 MERGERS, ETC. The Company shall not, directly or indirectly, enter
in any merger, consolidation or reorganization in which the Company shall not be
the surviving corporation unless the proposed surviving corporation shall, prior
to such merger, consolidation or reorganization, agree in writing to assume the
obligations of the Company under this Agreement and for that purpose references
hereunder to "Registrable Shares" shall be deemed to be references to the
securities which the Stockholders would be entitled to receive in exchange for
Registrable Shares under any such merger, consolidation or reorganization;
PROVIDED, HOWEVER, that the provisions of this Section 9.10 shall not apply in
the event of any merger, consolidation or reorganization in which the Company is
not the surviving corporation if all Institutional Stockholders are entitled to
receive in exchange for their Registrable Shares consideration consisting solely
of (i) cash, (ii) securities of the acquiring corporation which may be
immediately sold to the public without registration under the Securities Act, or
(iii) securities of the acquiring corporation which the acquiring corporation
has agreed to register within 90 days of completion of the transaction for
resale to the public pursuant to the Securities Act.

         9.11 TERMINATION OF REGISTRATION RIGHTS. All of the Company's
obligations to register Registrable Shares under this Agreement shall terminate
on the eighth anniversary of this Agreement. In addition, a Stockholder's
registration rights shall expire if (a) the Company has completed its Initial
Public Offering and is subject to the provisions of the Exchange Act, (b) all
Registrable Shares held by and issuable to such Stockholder (and its Affiliates,
partners, former partners, members and former members) may be sold under Rule
144 during any ninety (90) day period, and (c) Registrable Shares held by such
Stockholder equal less than one percent (1%) of the outstanding shares of Common
Stock (on an as-converted basis).

         9.12 TRANSFERS OF RIGHTS. The registration rights of each Institutional
Stockholder hereunder, along with its obligations related thereto, may be
assigned by such Institutional Stockholder, in whole or in part, to any person
or entity to which shares of Stock are transferred by such Institutional
Stockholder, and such transferee shall be deemed an "Institutional Stockholder"
for purposes of this Agreement generally and this Article 9 specifically)
provided that the Institutional Stockholder or the transferee provides written
notice of such assignment to the Company.

         9.13 REGISTRATION RIGHTS TO THIRD PARTIES. The Company shall not
without the written consent of the holders of at least two-thirds of the
Registrable Shares grant to any third party or group of parties rights with
respect to registration of shares of Stock under the Securities Act on terms
more favorable in the aggregate than those provided herein.

         9.14 CONSTRUCTION. For the purposes of this Article 9 only, the term
"Institutional Stockholders" shall be deemed to include Allergan Sales, Inc.
("Allergan Sales"), the successor to Vision Pharmaceuticals L.P., a Texas
limited partnership ("Vision"), and all references to


                                     24.

<PAGE>

"Registrable Shares" shall be deemed to include all "Registrable Securities"
as such term is used in the Stock Purchase Agreement dated September 24, 1997
between the Company and Vision. Allergan Sales represents and warrants that
it is the sole transferee of the rights, title and interests of Vision in the
Series C Preferred Stock.

                                   ARTICLE 10

                                   DEFINITIONS

         10.1 "Affiliate" means, with respect to any Person, any Person who
controls, is controlled by, or is under common control with, such Person.
"Affiliate" also means, with respect to ABN AMRO Ventures B.V., any venture
capital fund or other investment entity that is managed or advised by ABN AMRO
Ventures B.V. or any Affiliate thereof.

         10.2 "BankInvest" means BankInvest 7 Biotechnologi and BankInvest 1
Danske Aktier, collectively.

         10.3 "Board of Directors" means the board of directors of the Company.

         10.4 "Board Observer" has the meaning set forth in Section 7.3 of this
Agreement.

         10.5 "By-Laws" means the Company's By-Laws, as amended.

         10.6 "Certificate" means the Company's Certificate of Incorporation, as
amended and restated.

         10.7 "Commission" means the Securities and Exchange Commission, or any
other Federal agency at the time administering the Securities Act.

         10.8 "Common Stock" means the Common Stock, par value $.0001 per share,
of the Company.

         10.9 "Company" means ACADIA Pharmaceuticals Inc., its successors and
assigns.

         10.10 "Competitor" means any Person who conducts any business activity
of the same or similar kind as the Company or business activity in the
biotechnology, genetic engineering or pharmaceutical industries.

         10.11 "Copenhagen Project" means the Company's research and development
project which is more fully described in the Loan Commitment.

         10.12 "Corporation Law" means the General Corporation Law of the State
of Delaware, as amended.

         10.13 "Co-Sale Transaction" means either of the following events: (i)
shares of Stock representing a majority of the voting power of the Company
become beneficially owned by a single Person (including Affiliates of such
Person), or (ii) excluding shares issued in connection


                                      25.

<PAGE>

with a strategic relationship as set forth in Section 2.7(g), any shares of
Stock become beneficially owned by a Competitor or an Affiliate of a
Competitor.

         10.14 "Cure Period" has that meaning set forth in Section 5.2 of this
Agreement.

         10.15 "Event of Default" has that meaning set forth in Section 5.1 of
this Agreement.

         10.16 "Exchange Act" means the Securities Exchange Act of 1934, as
amended, or any similar Federal statute, and the rules and regulations of the
Commission issued under such Act, as they each may, from time to time, be in
effect.

         10.17 "Existing Institutional Stockholder" has that meaning set forth
in the introductory paragraph to this Agreement.

         10.18 "First Institutional Stockholders" means BankInvest, Dansk
Kapitalanlaeg Aktieselskab, Lonmodtagernes Dyrtidsfond and Kommunernes
Pensionsforsikring A/S.

         10.19 "First Stockholders Agreement" has that meaning set forth in
paragraph B of the Recitals.

         10.20 "First Amended Stockholders Agreement" has that meaning set forth
in paragraph C of the Recitals.

         10.21 "Founding Stockholder" means Mark R. Brann and shall not mean any
assignee or transferee of Mark R. Brann.

         10.22 "Initial Public Offering" means the closing of the Company's
first firm commitment underwritten public offering of its Common Stock under the
Securities Act.

         10.23 "Institutional Stockholder" has that meaning set forth in the
introductory paragraph of this Agreement.

         10.24 "Loan Commitment" means the commitment of Vaekstfonden to lend
the Company the sum of DKK 44,573,063.00.

         10.25 "Major Institutional Stockholder" means any Stockholder, other
than the Founding Stockholder, who owns at least 500,000 shares of Preferred
Stock. For purposes of this definition, all shares of Stock held by Affiliates
of a Stockholder will be aggregated to determine the number of shares of Stock
held by a Stockholder.

         10.26 "Major Stockholder" means each Major Institutional Stockholder
and the Founding Stockholder.

         10.27 "New Institutional Stockholder" has that meaning set forth in the
introductory paragraph to this Agreement.

         10.28 "Offered Securities" has that meaning set forth in Section 2.1 of
this Agreement.

         10.29 "Organizational Documents" means the Certificate and By-Laws.


                                     26.

<PAGE>

         10.30 "Partnership" means Investor Associates RT.

         10.31 "Person" means any individual, partnership (general or limited),
corporation, trust, estate, association, or other entity.

         10.32 "Preferred Stock" means the Series A Preferred Stock, Series B
Preferred Stock, Series C Preferred Stock, Series D Preferred Stock, Series E
Preferred Stock and any other series of preferred stock issued subsequent to the
date of this Agreement.

         10.33 "Qualifying IPO" has the meaning set forth in Section 2.7(f).

         10.34 "Registrable Shares" means (i) the shares of Common Stock issued
or issuable upon conversion of any Preferred Stock, (ii) the shares of Common
Stock into which the Preferred Stock (including Preferred Stock issued pursuant
to the Special Dividend) is reclassified, (iii) the shares of Common Stock
issued or issuable upon exercise of the Warrants, (iv) any shares of Common
Stock, and any shares of Common Stock issued or issuable upon the conversion or
exercise of any other securities, acquired by the Institutional Stockholders
pursuant to this Agreement, the Series A Stock Purchase Agreement, the Series B
Stock Purchase Agreement, the Series D Stock Purchase Agreement or the Series E
Stock Purchase Agreement and (v) any other shares of Common Stock issued in
respect of such shares (because of stock splits, stock dividends,
reclassifications, recapitalizations, or similar events); PROVIDED, HOWEVER,
that shares of Common Stock which are Registrable Shares shall cease to be
Registrable Shares (i) upon any sale pursuant to a Registration Statement or
Rule 144 under the Securities Act or (ii) upon any sale in any manner to a
person or entity which, by virtue of Section 9.12 of this Agreement, is not
entitled to the rights provided by this Agreement. Wherever reference is made in
this Agreement to a request or consent of holders of a certain percentage of
Registrable Shares, the determination of such percentage shall include shares of
Common Stock into which shares of Preferred Stock may be reclassified, including
that number of shares of Preferred Stock to which the applicable Stockholder
would be entitled following the declaration and issuance to the Special
Dividend.

         10.35 "Registration Expenses" means the expenses described in Section
9.4.

         10.36 "Registration Statement" means a registration statement filed by
the Company with the Commission for a public offering and sale of Common Stock
(other than a registration statement on Form S-8 or Form S-4, or their
successors, or any other form for a similar limited purpose, or any registration
statement covering only securities proposed to be issued in exchange for
securities or assets of another corporation).

         10.37 "Second Amended Stockholders Agreement" has the meaning set forth
in paragraph D of the Recitals.

         10.38 "Securities Act" means the Securities Act of 1933, as amended, or
any similar Federal statute, and the rules and regulations of the Commission
issued under such Act, as they each may, from time to time, be in effect.

         10.39 "Series A Preferred Stock" means the Series A Preferred Stock,
$0.01 par value per share, of the Company.


                                      27.
<PAGE>

         10.40 "Series B Preferred Stock" means the Series B Preferred Stock,
$0.01 par value per share, of the Company.

         10.41 "Series C Preferred Stock" means the Series C Preferred Stock,
$0.01 par value per share, of the Company.

         10.42 "Series D Preferred Stock" means the Series D Preferred Stock,
$0.01 par value per share, of the Company.

         10.43 "Series E Preferred Stock" means the Series E Preferred Stock,
$0.01 par value per share, of the Company.

         10.44 "Series A Stock Purchase Agreement" means the Series A Stock
Purchase Agreement between the Company, the Founding Stockholder and the First
Institutional Stockholders, dated February 3, 1997.

         10.45 "Series B Stock Purchase Agreement" means the Series B Stock
Purchase Agreement between and among the Company, the Founding Stockholder, the
Partnership and the First Institutional Stockholders, dated August 12, 1997.

         10.46 "Series C Stock Purchase Agreement" means the Stock Purchase
Agreement between the Company and Vision Pharmaceuticals L.P., dated September
24, 1997.

         10.47 "Series D Stock Purchase Agreement" means the Series D Preferred
Stock Purchase Agreement by and among the Company and the purchasers of the
Series D Preferred Stock, dated August 26, 1998.

         10.48 "Series E Stock Purchase Agreement" means the Series E Preferred
Stock Purchase Agreement by and among the Company and the purchasers of Series E
Preferred Stock, dated as of even date herewith.

         10.49 "Significant Actions" means any of the following actions:

                  (a) the authorization or issuance of any equity securities of
the Company, except for issuance of Common Stock in the manner contemplated by
Section 2.7(b), (c) (PROVIDED that such plan or arrangement is approved in
accordance with Section 10.49(e)) or (d);

                  (b) the declaration or payment of any dividend or any other
distribution, as defined in the Certificate, on Common Stock including without
limitation any stock dividend;

                  (c) making (or permitting an Affiliate of the Company to make)
a loan or advance to, or owning (or permitting an Affiliate of the Company to
own) any stock or other securities of, any subsidiary or other corporation,
partnership or other entity unless it is wholly owned by the Company;

                  (d) entering into a transaction with or for the benefit of any
Stockholder, officer or director of the Company or an Affiliate of any of the
foregoing;


                                     28.

<PAGE>

                  (e) the creation of any equity-based incentive compensation
plan or agreement described in Section 2.7(c) (other than the Company's 1997
Stock Option Plan) and the grant of more than 40,000, in the aggregate, options,
shares or rights thereunder;

                  (f) the guaranty, directly or indirectly, of any indebtedness
of another entity (including subsidiaries of the Company);

                  (g) the merger or consolidation of the Company with or into
another entity, the sale, lease or disposal of all or substantially all of the
assets of the Company, or the acquisition of all or substantially all of the
assets of another entity;

                  (h) a change in the fiscal year of the Company;

                  (i) the adoption or amendment of any policy governing the use,
protection, disclosure, enforcement or distribution of the intellectual property
of the Company;

                  (j) entering into, amending or terminating contracts in excess
of two years in length and involving, in the aggregate, expenditures by the
Company in excess of $150,000;

                  (k) commencing or resolving material litigation;

                  (l) creating or dissolving joint ventures, partnerships, or
subsidiaries;

                  (m) amending the Certificate or By-Laws, or changing the size
of the Board of Directors other than as contemplated by Section 6.1(a);

                  (n) resolving to dissolve or wind up the affairs of the
Company;

                  (o) using the proceeds of the investment made by the
Institutional Stockholders other than in accordance with a budget and business
plan approved by the Board of Directors by a Specified Majority;

                  (p) entering into, amending or terminating the employment
arrangement, including but not limited to written contracts of employment, with
any person who is, or is intended to become, an officer or key employee of the
Company with a base salary in excess of $150,000 per year, the grant of any
discretionary bonus or the approval of any bonus formula;

                  (q) approving the pledge of shares of Stock of the Company by
any Stockholder;

                  (r) waiving an affirmative covenant of the Company set forth
in Article 7 hereof;

                  (s) entering into, amending or terminating any material
contracts (including development contracts);

                  (t) the creation of any lien, pledge or other encumbrance on
any of assets of the Company or its subsidiaries other than as incurred in the
ordinary course of business;


                                      29.

<PAGE>

                  (u) the application for or acceptance of any European Union or
other public grants or subsidies including but not limited to grants or
subsidies for research purposes;

                  (v) acquisition, sale or other disposition of any assets
(other than Intellectual Property Rights) other than in the ordinary course of
business;

                  (w) acquisition, sale or other disposition of any Intellectual
Property Rights other than pursuant to licenses from or licenses to third
parties containing terms and conditions in substantial conformance with standard
terms and conditions for such licenses which have been approved by a Specified
Majority;

                  (x) the delegation of the authority of the Board of Directors,
including the authority to approve significant actions to any person or
committee;

                  (y) the purchase by the Company of any of its outstanding
securities;

                  (z) any material change to the basic strategy of the Company
as a biopharmaceutical company engaged in the discovery of lead compounds for
pharmaceutical development and related applications of its proprietary
technology platform that combines genome-based assays with high-throughput
screening and clinically relevant pharmacology;

                  (aa) the appointment or removal of the auditors of the
Company;

                  (bb) a material change in the accounting principles of the
Company;

                  (cc) any action whereby the Company would become a U.S. Real
Property Holding Company;

                  (dd) a sale or acquisition of any share in any corporate body;
or

                  (ee) any registration of the Company's Securities other than
in accordance with Article 9 hereof.

         10.50 "Significant Number of Stockholders" means at least all of the
Major Stockholders but one (1).

         10.51 "Special Dividend" has that meaning set forth in Section 2.1 of
this Agreement.

         10.52 "Specified Majority" means the affirmative vote of two-thirds of
the directors appointed by the Stockholders pursuant to Section 6.1(a), I.E. if
the number of directors appointed pursuant to Section 6.1(a) is eight (8), the
affirmative vote of six (6) directors and if the number of directors appointed
pursuant to Section 6.1(a) is nine (9), the affirmative vote of six (6)
directors.

         10.53 "Stock" means the issued and outstanding shares of Common Stock
and Preferred Stock.


                                     30.

<PAGE>

         10.54 "Subsidiary" means any entity 50% or more of whose securities are
owned by the Company or as to which the Company has the right to elect a
majority of the board of directors.

         10.55 "Third Amended Stockholders Agreement" has the meaning set forth
in paragraph E of the Recitals.

         10.56 "Warrants" means the Warrants held by certain Stockholders and
Allergan Sales , as the successor to Vision Pharmaceuticals L.P., as of the date
hereof.

                                   ARTICLE 11

                               GENERAL PROVISIONS

         11.1 LEGENDS.

                  (a) The following legends shall appear on the back of any
certificate for shares of Stock issued by the Company to the Stockholders:

                  THE SHARES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER
                  THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), AND MAY
                  NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, ASSIGNED,
                  PLEDGED OR HYPOTHECATED UNLESS (A) PURSUANT TO RULE 144 OR
                  RULE 144A UNDER THE ACT OR (B) THERE IS AN EFFECTIVE
                  REGISTRATION STATEMENT UNDER THE ACT COVERING SUCH SHARES OR
                  (C) THE COMPANY RECEIVES AN OPINION OF COUNSEL FOR THE HOLDER
                  OF THESE SHARES SATISFACTORY TO THE COMPANY AND ITS COUNSEL
                  STATING THAT SUCH SALE, TRANSFER, ASSIGNMENT, PLEDGE OR
                  HYPOTHECATION IS EXEMPT FROM THE REGISTRATION AND PROSPECTUS
                  DELIVERY REQUIREMENTS OF THE ACT.

                  THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO THE
                  TERMS OF A STOCKHOLDERS AGREEMENT AMONG THE COMPANY AND
                  CERTAIN OF ITS STOCKHOLDERS. ANY PURCHASER, ASSIGNEE,
                  TRANSFEREE, PLEDGEE OR OTHER SUCCESSOR TO ANY HOLDER HEREOF IS
                  BOUND BY THE TERMS OF SUCH AGREEMENT, A COPY OF WHICH WILL BE
                  MAILED, WITHOUT CHARGE, WITHIN FIVE (5) DAYS AFTER RECEIPT OF
                  A WRITTEN REQUEST THEREFOR DIRECTED TO THE SECRETARY OF THE
                  COMPANY.

                  (b) A legend substantially as set forth below shall appear on
the back of any certificate for shares of Stock issued to any person not a party
to this Agreement:

                  THE COMPANY AND CERTAIN OF ITS STOCKHOLDERS HAVE ENTERED INTO
                  A STOCKHOLDERS AGREEMENT THE TERMS OF WHICH MAY AFFECT THE
                  RIGHTS OF STOCKHOLDERS NOT


                                     31.

<PAGE>

                  A PARTY THERETO. THE COMPANY WILL MAIL A COPY OF SUCH
                  STOCKHOLDERS AGREEMENT TO ANY REGISTERED HOLDER OF ANY OF ITS
                  CAPITAL STOCK, WITHOUT CHARGE, WITHIN FIVE (5) DAYS AFTER A
                  WRITTEN REQUEST THEREFOR IS RECEIVED BY THE SECRETARY OF THE
                  COMPANY.

         11.2 AMENDMENT; TERMINATION. Except as otherwise provided specifically
in this Agreement, this Agreement may be amended or terminated only by a writing
which refers to this Agreement and which is executed by parties to this
Agreement holding 90% of the Stock or their permissible successors and assigns.
Notwithstanding the foregoing, (i) Articles 2, 3, 4, 5, 6, 7 and 8 of this
Agreement shall terminate and be of no further force and effect upon the closing
of a Qualifying IPO and (ii) this Agreement may be amended with only the written
consent of the Company to include additional purchasers of Series E Preferred
Stock as "New Institutional Stockholders" and "Stockholders" and parties hereto.

         11.3 EFFECT OF AGREEMENT. This Agreement shall be binding upon and
shall inure to the benefit of the Company and shall be binding upon and inure to
the benefit of the other parties hereto and any person who acquires shares of
Stock from the Company or from a party hereto in accordance with the terms of
this Agreement (including, without limitation, pursuant to the provisions of
Articles 2 and 3 of this Agreement). Except for the issuance by the Company of
shares and options pursuant to the Company's 1997 Stock Option Plan, the Company
shall not issue any certificate for shares of Stock to any person until such
person shall have first executed and delivered a copy of this Agreement. No
party to this Agreement may assign any of its rights or delegate any of its
duties under this Agreement except in connection with a transfer of its shares
of Stock which complies in all respects with the terms of this Agreement and the
Organizational Documents.

         11.4 COMPUTATION OF PERCENTAGES OR PRO RATA SHARE. All calculations or
determinations in this Agreement pertaining to percentage or pro rata interests
of holders of Preferred Stock shall be calculated on the basis of the number of
shares of Common Stock to which the holder of such Preferred Stock would be
entitled immediately prior to a public offering of Common Stock which causes a
reclassification or conversion of such Preferred Stock under Article IV, Section
C.5. of the Certificate at the date relevant for such determination or
calculation.

         11.5 COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original but all of which shall
constitute the same Agreement.

         11.6 NOTICES. All notices, elections and other communications pursuant
to this Agreement shall be made in writing and sent to (a) the Company at its
principal business address or (b) to any Stockholder at the address as shown on
the books and records of the Company and shall be deemed to be received the
second business day following deposit with an overnight mail or courier service,
the date of receipt of electronic confirmation of receipt of an electronic
facsimile message or one week after being sent by regular or certified mail,
postage prepaid.

         11.7 ENTIRE AGREEMENT. Except as expressly set forth herein or in an
instrument in writing signed by the party to be bound thereby which makes
reference to this Agreement, this


                                     32.

<PAGE>

Agreement embodies the entire agreement in relation to its subject matter,
and supersedes all prior agreements and negotiations.

         11.8 GOVERNING LAW. This Agreement shall in all respects be
interpreted, construed and governed by and in accordance with the internal
substantive law of the State of California.

         11.9 SEVERABILITY. Each Section, Article and lesser section of this
Agreement constitutes a separate and distinct undertaking, covenant and/or
provision hereof. In the event that any provision of is Agreement shall finally
be determined to be unlawful, all such provision shall be deemed severed from
this Agreement, but every other provision of this Agreement shall remain in full
force and effect, and in substitution for any such provision held unlawful,
there shall be substituted a provision of similar import reflecting the original
intent of the parties hereto to the extent permissible under law.

         11.10 CONSTRUCTION. The headings of the Articles and Sections of this
Agreement are inserted for convenience only and shall not be deemed to
constitute a part hereof. Unless otherwise specifically indicated, references in
is Agreement to Articles, Sections, paragraphs and clauses refer to the
Articles, Sections, paragraphs and clauses of this Agreement. All personal
pronouns used in this Agreement, whether used in the masculine, feminine or
neuter gender, shall include all other genders, and the singular shall include
the plural and vice versa.

         11.11 ARBITRATION. Any dispute, controversy or difference arising
between the parties out of or in relation to or in connection with this
Agreement or any breach thereof which cannot be settled between the parties
shall be finally settled under the Rules of Conciliation and Arbitration of the
International Chamber of Commerce (the "ICC") by which each party agrees to be
bound. In any arbitration pursuant to this Section the decision shall be
rendered by the three independent arbitrators who shall be appointed by the ICC
whose decision shall be binding. The seat of the arbitration shall be London,
England. The language of the arbitration shall be English.

                      [THIS SPACE INTENTIONALLY LEFT BLANK]


                                     33.


<PAGE>


         IN WITNESS WHEREOF, the parties to this Agreement, by their duly
authorized representatives and officers have executed this Agreement as of the
date and year first above written.

                                 COMPANY:

                                 ACADIA PHARMACEUTICALS INC.

                                 By: /s/ Leonard Borrmann
                                    --------------------------------------------
                                     Name: Leonard Borrmann
                                     Title: CEO


                                 FOUNDING STOCKHOLDER:

                                     /s/ Mark R. Brann
                                    --------------------------------------------
                                     MARK R. BRANN


                                 EXISTING INSTITUTIONAL STOCKHOLDERS:

                                 ABN AMRO VENTURES B.V.

                                 By: /s/ Fred Phillips
                                    --------------------------------------------
                                     Name: Fred Phillips
                                     Title:

                                 By: /s/ Mark Baldassare
                                    --------------------------------------------
                                     Name: Mark Baldassare
                                     Title: Investment Manager


                                 ALLMANNA PENSIONSFONDEN (5:AP)

                                 By: /s/ T. Nicolin
                                    --------------------------------------------
                                     Name: T. Nicolin
                                     Title: CEO



<PAGE>



                                 BANKINVEST 7 BIOTECHNOLOGI

                                 By: /s/ Finn Moefelt
                                    --------------------------------------------
                                     Name: Finn Moefelt
                                     Title: Man. Director


                                 BANKINVEST 1 DANSKE AKTIER

                                 By: /s/ Finn Moefelt
                                    --------------------------------------------
                                     Name: Finn Moefelt
                                     Title: Man. Director


                                 DANSK KAPITALANLAEG AKTIESELSKAB

                                 By: /s/ Arne J. Gillin
                                    --------------------------------------------
                                     Name: Arne J. Gillin
                                     Title: Vice President

                                 By: /s/ Niels K. Agner
                                    --------------------------------------------
                                     Name: Niels K. Agner
                                     Title: President


                                 KOMMUNERNES PENSIONSFORSIKRING A/S

                                 By: /s/ Jens Bisgaard-Flantlen
                                    --------------------------------------------
                                     Name: Jens Bisgaard-Flantlen
                                     Title: Head of Equities


                                 LARS HELLERUNG CHRISTIANSEN

                                 By: /s/ Lars Hellerung Christiansen
                                    --------------------------------------------
                                     Name:
                                     Title:


<PAGE>


                                 LONMODTAGERNES DYRTIDSFOND

                                 By: /s/ Hans Jorgen Madsen
                                    --------------------------------------------
                                     Name: Hans Jorgen Madsen
                                     Title: Head of Department

                                 By: /s/ Anita Klitgaard
                                    --------------------------------------------
                                     Name: Anita Klitgaard
                                     Title: Secretary


                                 SVENSKA HANDELSBANKEN (GOTEBORG)

                                 By: /s/ E e-Britt Jarfelt
                                    --------------------------------------------
                                     Name: E e-Britt Jarfelt
                                     Title: Senior Vice President

                                 By: /s/ Mats Littorin
                                    --------------------------------------------
                                     Name: Mats Littorin
                                     Title: Vice President and General Counsel


                                 SVENSKA HANDELSBANKEN (MALMO)

                                 By: /s/ Jorna Olycampus
                                    --------------------------------------------
                                     Name:
                                     Title:




<PAGE>



                                 NEW INSTITUTIONAL STOCKHOLDERS:


                                 H&Q LIFE SCIENCES INVESTORS

                                 By: /s/ Alan G. Carr
                                    --------------------------------------------
                                     Name: Alan G. Carr
                                     Title: President


                                 H&Q HEALTHCARE INVESTORS

                                 By: /s/ Alan G. Carr
                                    --------------------------------------------
                                     Name: Alan G. Carr
                                     Title: President


                                 THE KAUFMANN FUND

                                 By: /s/ Lawrence Aumard
                                    --------------------------------------------
                                     Name: Lawrence Aumard
                                     Title: Chairman


                                 EATON VANCE WORLDWIDE HEALTH SCIENCES FUND

                                 By: /s/ Samuel D. Isaly
                                    --------------------------------------------
                                     Name: Samuel D. Isaly
                                     Title: Portfolio Manager


                                 FINSBURY WORLDWIDE PHARMACEUTICAL TRUST

                                 By: /s/ Samuel D. Isaly
                                    --------------------------------------------
                                     Name: Samuel D. Isaly
                                     Title: Portfolio Manager




<PAGE>



                                 LIFE SCIENCE NO. 1 INVESTMENT PARTNERSHIP

                                 By: /s/ David J. Drutz
                                    --------------------------------------------
                                     Name: David J. Drutz
                                     Title: Partner


                                 LIFE SCIENCE NO. 2 INVESTMENT PARTNERSHIP

                                 By: /s/ David J. Drutz
                                    --------------------------------------------
                                     Name: David J. Drutz
                                     Title: Partner


                                 LIFE SCIENCE NO. 3 INVESTMENT PARTNERSHIP

                                 By: /s/ David J. Drutz
                                    --------------------------------------------
                                     Name: David J. Drutz
                                     Title: Partner


<PAGE>



                                 FOR PURPOSES OF ARTICLE 9 ONLY:

                                 ALLERGAN SALES, INC.


                                 BY: /s/ George Lasezkay
                                    --------------------------------------------
                                 NAME: George Lasezkay
                                      ------------------------------------------
                                 TITLE: Vice President
                                       -----------------------------------------