<PAGE>

                                                                  Exhibit 4.5

                           [ARENA PHARMACEUTICALS LOGO]


                           ARENA PHARMACEUTICALS, INC.

                   2001 ARENA EMPLOYEE STOCK PURCHASE PLAN


        The following constitutes the provisions of the 2001 Arena Employee
Stock Purchase Plan.

        1. PURPOSE. The purpose of the Plan is to provide employees of Arena
Pharmaceuticals, Inc. (the "Company") and its Designated Subsidiaries with an
opportunity to purchase Common Stock of the Company through accumulated
payroll deductions. It is the intention of the Company to have the Plan
qualify as an "Employee Stock Purchase Plan" under Section 423 of the
Internal Revenue Code of 1986, as amended. The provisions of the Plan,
accordingly, shall be construed so as to extend and limit participation in a
manner consistent with the requirements of that section of the Code.

        2. DEFINITIONS.

               (a) "Board"  shall  mean  the  Board of  Directors  of
the Company.

               (b) "Code" shall mean the Internal Revenue Code of 1986, as
amended. References to specific sections of the Code shall be taken to be
references to corresponding sections of any successor statute.

               (c) "Common  Stock"  shall  mean the  common  stock of
the Company.

               (d) "Company" shall mean Arena  Pharmaceuticals,  Inc.,
or any successor by merger or  otherwise,  and any  Designated  Subsidiary of
the Company.

               (e) "Compensation" shall mean all base gross earnings,
commissions, overtime, shift premium, incentive compensation, incentive
payments, and bonuses before giving effect to any compensation reductions
made in connection with plans described in section 401(k) or 125 of the Code,
but exclusive of payments for any other compensation.


                                       1
<PAGE>

               (f) "Designated Subsidiary" shall mean any Subsidiary that has
been designated by the Board from time to time in its sole discretion as
eligible to participate in the Plan. For purposes of the Plan, BRL Screening,
Inc. shall be deemed to have been designated by the Board as a Designated
Subsidiary.

               (g) "Employee" shall mean any individual who is an Employee of
the Company for tax purposes whose customary employment with the Company is
at least twenty (20) hours per week. For purposes of the Plan, the employment
relationship shall be treated as continuing intact while the individual is on
sick leave or other leave of absence approved by the Company. Where the
period of leave exceeds 90 days and the individual's right to reemployment is
not guaranteed either by statute or by contract, the employment relationship
shall be deemed to have terminated on the 91st day of such leave.

               (h) "Enrollment  Date" shall mean the first Trading Day
of each Offering Period.

               (i) "Exercise  Date"  shall mean the last  Trading  Day
of each Purchase Period.

               (j) "Fair Market  Value" shall mean,  as of any date,
the value of Common Stock determined as follows:

                      (1)     If  the   Common   Stock   is   listed   on
any established stock exchange or a national market system, including without
limitation the Nasdaq National Market or The Nasdaq SmallCap Market of The
Nasdaq Stock Market, its Fair Market Value shall be the closing sales price
for such stock (or the closing bid, if no sales were reported) as quoted on
such exchange or system for the last market trading day on the date of such
determination, as reported in THE WALL STREET JOURNAL or such other source as
the Board deems reliable;

                      (2)     If the  Common  Stock is  regularly  quoted by
a recognized securities dealer but selling prices are not reported, its Fair
Market Value shall be the mean of the closing bid and asked prices for the
Common Stock on the date of such determination, as reported in THE WALL
STREET JOURNAL or such other source as the Board deems reliable; or

                      (3)     In the absence of an established  market for
the Common Stock, the Fair Market Value thereof shall be determined in good
faith by the Board.

               (k) "Offering Periods" shall mean the periods of approximately
twenty-four (24) months during which an option granted pursuant to the Plan
may be exercised, commencing on the first Trading Day on or after January 1,
April 1, July 1, and October 1 of each year and terminating on the last
Trading Day in the periods ending twenty-four months later. The first
Offering Period shall be the period commencing July 1, 2001 and terminating
on the last Trading Day on or before June 30, 2003. The duration and timing
of Offering Periods may be changed pursuant to Section 4 of this Plan.


                                       2
<PAGE>

               (l) "Plan" shall mean this 2001 Arena Employee Stock Purchase
Plan.

               (m) "Purchase Period" shall mean the approximately three (3)
month period commencing on the next Trading Day following the preceding
Exercise Date and ending with the next Exercise Date, except that the first
Purchase Period of any Offering Period shall commence on the Enrollment Date
and end with the next Exercise Date.

               (n) "Purchase Price" shall mean 85% of the Fair Market Value
of a share of Common Stock on the Enrollment Date or on the Exercise Date,
whichever is lower; provided however, that the Purchase Price may be adjusted
by the Board pursuant to Section 20.

               (o) "Reserves" shall mean the number of shares of Common Stock
covered by each option under the Plan that have not yet been exercised and
the number of shares of Common Stock which have been authorized for issuance
under the Plan but not yet placed under option.

               (p) "Subsidiary" shall mean a corporation, domestic or
foreign, of which not less than 50% of the voting shares are held by the
Company or a Subsidiary, whether or not such corporation now exists or is
hereafter organized or acquired by the Company or a Subsidiary.

               (q) "Trading Day" shall mean a day on which national stock
exchanges and the Nasdaq System are open for trading.

        3. ELIGIBILITY.

               (a) Any Employee who shall be employed by the Company on a
given Enrollment Date shall be eligible to participate in the Plan.

               (b) Any provisions of the Plan to the contrary
notwithstanding, no Employee shall be granted an option under the Plan (i) to
the extent that, immediately after the grant, such Employee (or any other
person whose stock would be attributed to such Employee pursuant to Section
424(d) of the Code) would own capital stock of the Company and/or hold
outstanding options to purchase such stock possessing five percent (5%) or
more of the total combined voting power or value of all classes of the
capital stock of the Company or of any parent or subsidiary corporation, or
(ii) to the extent that his or her rights to purchase stock under all
employee stock purchase plans of the Company and any parent or subsidiary
corporation accrues at a rate which exceeds Twenty-Five Thousand Dollars
($25,000) worth of stock (determined at the fair market value of the shares
at the time such option is granted) for each calendar year in which such
option is outstanding at any time.


                                       3
<PAGE>

        4. OFFERING PERIODS.

               (a) PLAN IMPLEMENTATION. The Plan shall be implemented by
consecutive, overlapping Offering Periods with a new Offering Period
commencing on the first Trading Day on or after January 1, April 1, July 1,
and October 1 of each year, or on such other date as the Board (or its
committee appointed pursuant to Section 14) shall determine, and continuing
thereafter until terminated in accordance with Section 20 hereof. The first
Offering Period shall begin on July 1, 2001 and, except as may be otherwise
provided for in Section 4(c), shall end on the last Trading Day on or before
June 30, 2003. The Board shall have the power to change the duration of
Offering Periods (including the commencement dates thereof) with respect to
future offerings without stockholder approval if such change is announced
prior to the scheduled beginning of the first Offering Period to be affected
thereafter.

               (b) OFFERING PERIOD DURATION. Each Offering Period shall be
for a period of approximately twenty-four (24) months during which an option
granted pursuant to the Plan may be exercised.

               (c) AUTOMATIC TRANSFER TO LOW PRICE OFFERING PERIOD. To the
extent permitted by any applicable laws, regulations, stock exchange rules,
or Nasdaq Stock Market rules, if the Fair Market Value of the Common Stock on
any Exercise Date in an Offering Period is lower than the Fair Market Value
of the Common Stock on the Enrollment Date of such Offering Period, then all
participants in such Offering Period shall be automatically withdrawn from
such Offering Period immediately after the exercise of their option on such
Exercise Date and automatically re-enrolled in the immediately following
Offering Period as of the first day thereof.

               (d) CHANGES BY BOARD. The Board shall have the power to change
the duration of Offering Periods (including the commencement dates thereof)
with respect to future offerings without stockholder approval if such change
is announced prior to the scheduled beginning of the first Offering Period to
be affected thereafter.

        5. PARTICIPATION.

               (a) An eligible Employee may become a participant in the Plan
by completing a subscription agreement authorizing payroll deductions in the
form of EXHIBIT A attached to this Plan and filing it with the Company's
payroll office prior to the applicable Enrollment Date.

               (b) Payroll deductions for a participant shall commence on the
first payroll following the Enrollment Date and shall end on the last payroll
in the Offering Period to which such authorization is applicable, unless
sooner terminated by the participant as provided in Section 10 hereof.


                                       4
<PAGE>

        6. PAYROLL DEDUCTIONS.

               (a) At the time a participant files his or her subscription
agreement, he or she shall elect to have payroll deductions made on each pay
day during the Offering Period in an amount not exceeding fifteen percent
(15%) of the Compensation which he or she receives on each pay day during the
Offering Period.

               (b) All payroll deductions made for a participant shall be
credited to his or her account under the Plan and shall be withheld in whole
percentages only. A participant may not make any additional payments into
such account.

               (c) A participant may discontinue his or her participation in
the Plan as provided in Section 10 hereof, or may increase or decrease the
rate of his or her payroll deductions during the Offering Period by
completing or filing with the Company's payroll office a new subscription
agreement authorizing a change in payroll deduction rate. The Board may, in
its discretion, limit the number of participation rate changes during any
Offering Period. The change in rate shall be effective with the first full
payroll period following five (5) business days after the Company's receipt
of the new subscription agreement unless the Company elects to process a
given change in participation more quickly. A participant's subscription
agreement shall remain in effect for successive Offering Periods unless
terminated as provided in Section 10 hereof.

               (d) Notwithstanding the foregoing, to the extent necessary to
comply with Section 423(b)(8) of the Code and Section 3(b) hereof, a
participant's payroll deductions may be decreased to zero percent (0%) at any
time during a Purchase Period. Payroll deductions shall recommence at the
rate provided in such participant's subscription agreement at the beginning
of the first Purchase Period that is scheduled to end in the following
calendar year, unless terminated by the participant as provided in Section 10
hereof.

               (e) At the time the option is exercised, in whole or in part,
or at the time some or all of the Company's Common Stock issued under the
Plan is disposed of, the participant must make adequate provision for the
Company's federal, state, or other tax withholding obligations, if any, which
arise upon the exercise of the option or the disposition of the Common Stock.
At any time, the Company may, but shall not be obligated to, withhold from
the participant's compensation the amount necessary for the Company to meet
applicable withholding obligations, including any withholding required to
make available to the Company any tax deductions or benefits attributable to
sale or early disposition of Common Stock by the Employee.

        7. GRANT OF OPTION. On the Enrollment Date of each Offering Period,
each eligible Employee participating in such Offering Period shall be granted
an option to purchase on each Exercise Date during such Offering Period (at
the applicable Purchase Price) up to a number of shares of the Company's
Common Stock determined by dividing such Employee's payroll deductions
accumulated prior to such Exercise Date and retained


                                       5
<PAGE>

in the Participant's account as of the Exercise Date by the applicable
Purchase Price; provided that in no event shall an Employee be permitted to
purchase during each Purchase Period more than Six Hundred Twenty Five (625)
shares of the Company's Common Stock (subject to any adjustment pursuant to
Section 19), and provided further that such purchase shall be subject to the
limitations set forth in Sections 3(b) and 12 hereof. The Board may, for
future Offering Periods, increase or decrease, in its absolute discretion,
the maximum number of shares of the Company's Common Stock an Employee may
purchase during each Purchase Period of such Offering Period. Exercise of the
option shall occur as provided in Section 8 hereof, unless the participant
has withdrawn pursuant to Section 10 hereof. The option shall expire on the
last day of the Offering Period.

        8. EXERCISE OF OPTION.

               (a) Unless a participant withdraws from the Plan as provided
in Section 10 hereof, his or her option for the purchase of shares shall be
exercised automatically on the Exercise Date, and the maximum number of full
shares subject to the option shall be purchased for such participant at the
applicable Purchase Price with the accumulated payroll deductions in his or
her account. No fractional shares shall be purchased; any payroll deductions
accumulated in a participant's account which are not sufficient to purchase a
full share shall be retained in the participant's account for the subsequent
Purchase Period or Offering Period, subject to earlier withdrawal by the
participant as provided in Section 10 hereof. Any other monies left over in a
participant's account after the Exercise Date shall be returned to the
participant. During a participant's lifetime, a participant's option to
purchase shares hereunder is exercisable only by him or her.

               (b) If the Board determines that, on a given Exercise Date,
the number of shares with respect to which options are to be exercised may
exceed (i) the number of shares of Common Stock that were available for sale
under the Plan on the Enrollment Date of the applicable Offering Period, or
(ii) the number of shares available for sale under the Plan on such Exercise
Date, the Board may in its sole discretion (x) provide that the Company shall
make a pro rata allocation of the shares of Common Stock available for
purchase on such Enrollment Date or Exercise Date, as applicable, in as
uniform a manner as shall be practicable and as it shall determine in its
sole discretion to be equitable among all participants exercising options to
purchase Common Stock on such Exercise Date, and continue all Offering
Periods then in effect, or (y) provide that the Company shall make a pro rata
allocation of the shares available for purchase on such Enrollment Date or
Exercise Date, as applicable, in as uniform a manner as shall be practicable
and as it shall determine in its sole discretion to be equitable among all
participants exercising options to purchase Common Stock on such Exercise
Date, and terminate any or all Offering Periods then in effect pursuant to
Section 20 hereof. The Company may make pro rata allocations of the shares
available on the Enrollment Date of any applicable Offering Period pursuant
to the preceding sentence, notwithstanding any authorization of additional
shares for issuance under the Plan by the Company's stockholders subsequent
to such Enrollment Date.


                                       6
<PAGE>

        9. DELIVERY.    As promptly as  practicable  after each  Exercise
Date on which a purchase of shares  occurs,  the Company shall arrange the
delivery to each participant,  as appropriate, of a certificate representing
the shares purchased upon exercise of his or her option.

        10. WITHDRAWAL.

               (a) A participant may withdraw all but not less than all the
payroll deductions credited to his or her account and not yet used to
exercise his or her option under the Plan at any time by giving written
notice to the Company's payroll office in the form of EXHIBIT B attached to
this Plan. All of the participant's payroll deductions credited to his or her
account shall be paid to such participant promptly after receipt of notice of
withdrawal and such participant's option for the Offering Period shall be
automatically terminated, and no further payroll deductions for the purchase
of shares shall be made for such Offering Period. If a participant withdraws
from an Offering Period, payroll deductions shall not resume at the beginning
of the succeeding Offering Period unless the participant delivers to the
Company's payroll office a new subscription agreement.

               (b) A participant's withdrawal from an Offering Period shall
not have any effect upon his or her eligibility to participate in any similar
plan that may hereafter be adopted by the Company or in succeeding Offering
Periods that commence after the termination of the Offering Period from which
the participant withdraws.

        11. TERMINATION OF EMPLOYMENT.   Upon a participant's ceasing to be
an Employee, for any reason, he or she shall be deemed to have elected to
withdraw from the Plan and the payroll deductions credited to such
participant's account during the Offering Period but not yet used to exercise
the option shall be returned to such participant or, in the case of his or
her death, to the person or persons entitled thereto under Section 15 hereof,
and such participant's option shall be automatically terminated.

        12. INTEREST.   No interest shall accrue on the payroll deductions
of a participant in the Plan.

        13. STOCK.

               (a) Subject to adjustment upon changes in capitalization of
the Company as provided in Section 19 hereof, the maximum number of shares of
the Company's Common Stock which shall be made available for sale under the
Plan shall be One Million (1,000,000) shares.

               (b) The participant shall have no interest or voting rights in
shares covered by his or her option until such option has been exercised.


                                       7
<PAGE>

               (c) Shares  to be  delivered  to a  participant  under
the Plan shall be registered in the name of the  participant or in the name
of the participant and his or her spouse.

        14. ADMINISTRATION. The Plan shall be administered by the Board or a
committee of members of the Board appointed by the Board. The Board or its
committee shall have full and exclusive discretionary authority to construe,
interpret and apply the terms of the Plan, to determine eligibility and to
adjudicate all disputed claims filed under the Plan. Every finding, decision
and determination made by the Board or its committee shall, to the full
extent permitted by law, be final and binding upon all parties.

        15. DESIGNATION OF BENEFICIARY.

               (a) A participant may file with the Company's payroll office a
written designation of a beneficiary who is to receive any shares and cash
from the participant's account under the Plan in the event of such
participant's death subsequent to an Exercise Date on which the option is
exercised but prior to delivery to such participant of such shares and cash.
In addition, a participant may file with the Company's payroll office a
written designation of a beneficiary who is to receive any cash from the
participant's account under the Plan in the event of such participant's death
prior to the exercise of the option. If a participant is married and the
designated beneficiary is not the spouse, spousal consent shall be required
for such designation to be effective.

               (b) Such designation of beneficiary may be changed by the
participant at any time by written notice. In the event of the death of a
participant and in the absence of a beneficiary validly designated under the
Plan who is living at the time of such participant's death, the Company shall
deliver such shares and/or cash to the executor or administrator of the
estate of the participant, or if no such executor or administrator has been
appointed (to the knowledge of the Company), the Company, in its discretion,
may deliver such shares and/or cash to the spouse or to any one or more
dependents or relatives of the participant, or if no spouse, dependent or
relative is known to the Company, then to such other person as the Company
may designate.

        16. TRANSFERABILITY. Neither payroll deductions credited to a
participant's account nor any rights with regard to the exercise of an option
or to receive shares under the Plan may be assigned, transferred, pledged or
otherwise disposed of in any way (other than by will, the laws of descent and
distribution or as provided in Section 15 hereof) by the participant. Any
such attempt at assignment, transfer, pledge or other disposition shall be
without effect, except that the Company may treat such act as an election to
withdraw funds from an Offering Period in accordance with Section 10 hereof.

        17. USE OF FUNDS. All payroll  deductions  received or held by
the Company under the Plan may be used by the Company for any  corporate
purpose, and the Company shall not be obligated to segregate such payroll
deductions.

        18. REPORTS. Individual accounts shall be maintained for each
participant in the Plan. Statements of account shall be given to
participating Employees at least annually,


                                       8
<PAGE>

which statements shall set forth the amounts of payroll deductions, the
Purchase Price, the number of shares purchased and the remaining cash
balance, if any.

        19. ADJUSTMENTS UPON CHANGES IN CAPITALIZATION,
        DISSOLUTION, LIQUIDATION, MERGER OR ASSET SALE.

               (a) CHANGES IN CAPITALIZATION. Subject to any required action
by the stockholders of the Company, the Reserves, the maximum number of
shares each participant may purchase each Purchase Period (pursuant to
Section 7), as well as the price per share and the number of shares of Common
Stock covered by each option under the Plan which have not yet been exercised
shall be proportionately adjusted for any increase or decrease in the number
of issued shares of Common Stock resulting from a stock split, reverse stock
split, stock dividend, combination or reclassification of the Common Stock,
or any other increase or decrease in the number of shares of Common Stock
effected without receipt of consideration by the Company; provided, however,
that conversion of any convertible securities of the Company shall not be
deemed to have been "effected without receipt of consideration". Such
adjustment shall be made by the Board, whose determination in that respect
shall be final, binding and conclusive. Except as expressly provided herein,
no issuance by the Company of shares of stock of any class, or securities
convertible into shares of stock of any class, shall affect, and no
adjustment by reason thereof shall be made with respect to, the number or
price of shares of Common Stock subject to an option.

               (b) DISSOLUTION OR LIQUIDATION. In the event of a proposed
dissolution or liquidation of the Company, the Offering Period then in
progress shall be shortened by setting a new Exercise Date (the "New Exercise
Date"), and shall terminate immediately prior to the consummation of such
proposed dissolution or liquidation, unless provided otherwise by the Board.
The New Exercise Date shall be before the date of the Company's proposed
dissolution or liquidation. The Board shall notify each participant in
writing, at least ten (10) business days prior to the New Exercise Date, that
the Exercise Date for the participant's option has been changed to the New
Exercise Date and that the participant's option shall be exercised
automatically on the New Exercise Date, unless prior to such date the
participant has withdrawn from the Offering Period as provided in Section 10
hereof.

               (c) MERGER OR ASSET SALE. In the event of a proposed sale of
all or substantially all of the assets of the Company, or the merger of the
Company with or into another corporation, each outstanding option shall be
assumed or an equivalent option substituted by the successor corporation or a
parent or subsidiary of the successor corporation. In the event that the
successor corporation refuses to assume or substitute for the option, any
Purchase Periods then in progress shall be shortened by setting a new
Exercise Date (the "New Exercise Date") and any Offering Periods then in
progress shall end on the New Exercise Date. The New Exercise Date shall be
before the date of the Company's proposed sale or merger. The Board shall
notify each participant in writing, at least ten (10) business days prior to
the New Exercise Date, that the Exercise Date for the participant's option
has been changed to the New Exercise Date and that the participant's


                                       9
<PAGE>

option shall be exercised automatically on the New Exercise
Date, unless prior to such date the participant has withdrawn from the
Offering Period as provided in Section 10 hereof.

        20. AMENDMENT OR TERMINATION.

               (a) The Board of Directors of the Company may at any time and
for any reason terminate or amend the Plan. Except as provided in Section 19
hereof, no such termination can affect options previously granted, provided
that an Offering Period may be terminated by the Board of Directors on any
Exercise Date if the Board determines that the termination of the Offering
Period or the Plan is in the best interests of the Company and its
stockholders. Except as provided in Section 19 and this Section 20 hereof, no
amendment may make any change in any option theretofore granted which
adversely affects the rights of any participant. To the extent necessary to
comply with Section 423 of the Code (or any successor rule or provision or
any other applicable law, regulation or Nasdaq stock market rule or stock
exchange rule), the Company shall obtain stockholder approval in such a
manner and to such a degree as required.

               (b) Without stockholder consent and without regard to whether
any participant rights may be considered to have been "adversely affected,"
the Board (or its committee appointed pursuant to Section 14) shall be
entitled to change the Offering Periods, limit the frequency and/or number of
changes in the amount withheld during an Offering Period, establish the
exchange ratio applicable to amounts withheld in a currency other than U.S.
dollars, permit payroll withholding in excess of the amount designated by a
participant in order to adjust for delays or mistakes in the Company's
processing of properly completed withholding elections, establish reasonable
waiting and adjustment periods and/or accounting and crediting procedures to
ensure that amounts applied toward the purchase of Common Stock for each
participant properly correspond with amounts withheld from the participant's
Compensation, and establish such other limitations or procedures as the Board
(or its committee) determines in its sole discretion advisable which are
consistent with the Plan.

               (c) In the event the Board determines that the ongoing
operation of the Plan may result in unfavorable financial accounting
consequences, the Board may, in its discretion and, to the extent necessary
or desirable, modify or amend the Plan to reduce or eliminate such accounting
consequences including, but not limited to:

                      (1) altering the Purchase Price for any Offering
Period including an Offering Period underway at the time of the change
in Purchase Price;

                      (2) shortening any Offering Period so that the
Offering Period ends on a new Exercise Date, including an Offering Period
underway at the time of the Board action; and

                      (3) allocating shares.


                                       10
<PAGE>

Such modifications or amendments shall not require stockholder approval or
the consent of any Plan participants.

        21. NOTICES. All notices or other communications by a participant to
the Company under or in connection with the Plan shall be deemed to have been
duly given when received in the form specified by the Company at the
location, or by the person, designated by the Company for the receipt thereof.

        22. CONDITIONS UPON ISSUANCE OF SHARES. Shares shall not be issued
with respect to an option unless the exercise of such option and the issuance
and delivery of such shares pursuant thereto shall comply with all applicable
provisions of law, domestic or foreign, including, without limitation, the
Securities Act of 1933, as amended, the Securities Exchange Act of 1934, as
amended, the rules and regulations promulgated thereunder, and the
requirements of the Nasdaq Stock Market or any stock exchange upon which the
shares may then be listed, and shall be further subject to the approval of
counsel for the Company with respect to such compliance. As a condition to
the exercise of an option, the Company may require the person exercising such
option to represent and warrant at the time of any such exercise that the
shares are being purchased only for investment and without any present
intention to sell or distribute such shares if, in the opinion of counsel for
the Company, such a representation is required by any of the aforementioned
applicable provisions of law.

        23. TERM OF PLAN. The Plan shall become effective upon
the earlier to occur of its adoption by the Board of Directors or its
approval by the stockholders of the Company. It shall continue in effect
for a term of ten (10) years unless sooner terminated under Section 20 hereof.

        24. MISCELLANEOUS.

        (a) ADMINISTRATIVE COSTS. The Company shall pay the administrative
expenses associated with the operation of the Plan (other than brokerage
commissions resulting from sales of Common Stock directed by Employees).

        (b) NO EMPLOYMENT RIGHTS. Participation in the Plan shall not give an
Employee any right to continue in the employment of the Company, and shall
not affect the right of the Company to terminate the Employee's employment at
any time, with or without cause.

        (c) REPURCHASE OF STOCK. The Company shall not be required to
purchase or repurchase from any Employee any of the shares of Common Stock
that the Employee acquires under the Plan.

        (d) INTERNAL REVENUE CODE AND ERISA CONSIDERATIONS. The Plan is
intended to constitute an "employee stock purchase plan" within the meaning
of section 423 of the Internal Revenue Code of 1986, as amended, and the
regulations thereunder. The provisions of the Plan, accordingly, shall be
construed so as to comply with the requirements of that section of the Code
or any successor provision, and the regulations


                                       11
<PAGE>

thereunder. The Plan is not intended and shall not be construed as
constituting an "employee benefit plan," within the meaning of section 3(3)
of the Employee Retirement Income Security Act of 1974, as amended.

        (e) HEADINGS, CAPTIONS, GENDER. The headings and captions herein
are for convenience of reference only and shall not be considered as part
of the text. The masculine shall include the feminine, and vice versa.

        (f) SEVERABILITY OF PROVISIONS, PREVAILING LAW. The provisions of the
Plan shall be deemed severable. In the event any such provision is determined
to be unlawful or unenforceable by a court of competent jurisdiction or by
reason of a change in an applicable statute, the Plan shall continue to exist
as though such provision had never been included therein (or, in the case of
a change in an applicable statute, had been deleted as of the date of such
change). The Plan shall be governed by the laws of the State of California to
the extent such laws are not in conflict with, or superseded by, federal law.

                                  [END OF PLAN]


                                       12
<PAGE>

                           [ARENA PHARMACEUTICALS LOGO]

                           ARENA PHARMACEUTICALS, INC.


                                    EXHIBIT A

                   2001 ARENA EMPLOYEE STOCK PURCHASE PLAN

                            *SUBSCRIPTION AGREEMENT*


_____ Original Application                       Enrollment Date: ___________
_____ Change in Payroll Deduction Rate
_____ Change of Beneficiary(ies)


1.    __________________________ hereby elects to participate in the 2001 Arena
      Employee Stock Purchase Plan (the "Employee Stock Purchase Plan") and
      subscribes to purchase shares of the Company's Common Stock in accordance
      with this Subscription Agreement and the Employee Stock Purchase Plan.

2.    I hereby authorize payroll deductions from each paycheck in the amount of
      ____% of my Compensation on each payday (from 1 to 15%) during the
      Offering Period in accordance with the Employee Stock Purchase Plan.
      (PLEASE NOTE that no fractional percentages are permitted.)

3.    I understand that said payroll deductions shall be accumulated for the
      purchase of shares of Common Stock at the applicable Purchase Price
      determined in accordance with the Employee Stock Purchase Plan. I
      understand that if I do not withdraw from an Offering Period, any
      accumulated payroll deductions will be used to automatically exercise my
      option.

4.    I have received a copy of the complete Employee Stock Purchase Plan. I
      understand that my participation in the Employee Stock Purchase Plan is in
      all respects subject to the terms of the Plan. I understand that my
      ability to exercise the option under this Subscription Agreement is
      subject to stockholder approval of the Employee Stock Purchase Plan.


                                       13
<PAGE>

5.    Shares purchased for me under the Employee Stock Purchase Plan should be
      issued in the name(s) of (Employee or Employee and Spouse only):
      _____________________________; _____________________________________.

6.    I understand that if I dispose of any shares received by me pursuant to
      the Plan within 2 years after the Enrollment Date (the first day of the
      Offering Period during which I purchased such shares) or one year after
      the Exercise Date, I will be treated for federal income tax purposes as
      having received ordinary income at the time of such disposition in an
      amount equal to the excess of the fair market value of the shares at
      the time such shares were purchased by me over the price which I paid
      for the shares. I hereby agree to notify the Company in writing
      immediately or within 10 days after the date of any disposition of my
      shares and I will make adequate provision for Federal, state or other
      tax withholding obligations, if any, which arise upon the disposition
      of the Common Stock. The Company may, but will not be obligated to,
      withhold from my compensation the amount necessary to meet any
      applicable withholding obligation including any withholding necessary
      to make available to the Company any tax deductions or benefits
      attributable to sale or early disposition of Common Stock by me. If I
      dispose of such shares at any time after the expiration of the 2-year
      and 1-year holding periods, I understand that I will be treated for
      federal income tax purposes as having received income only at the time
      of such disposition, and that such income will be taxed as ordinary
      income only to the extent of an amount equal to the lesser of (1) the
      excess of the fair market value of the shares at the time of such
      disposition over the purchase price which I paid for the shares, or (2)
      15% of the fair market value of the shares on the first day of the
      Offering Period. The remainder of the gain, if any, recognized on such
      disposition will be taxed as capital gain.

7.    I hereby agree to be bound by the terms of the Employee Stock Purchase
      Plan. The effectiveness of this Subscription Agreement is dependent upon
      my eligibility to participate in the Employee Stock Purchase Plan.


                                       14
<PAGE>

8.    In the event of my death, I hereby designate the following as my
      beneficiary(ies) to receive all payments and shares due me under the
      Employee Stock Purchase Plan:

NAME:  (Please print)


      _________________________________________________________________________
          (First)                 (Middle)                            (Last)

      _______________________________________
      Relationship to Employee

ADDRESS:

____________________________________

____________________________________

____________________________________

Employee's Social
Security Number:              ____________________________________


Employee's Address:           ____________________________________

                              ____________________________________

                              ____________________________________


I UNDERSTAND THAT THIS SUBSCRIPTION AGREEMENT SHALL REMAIN IN EFFECT
THROUGHOUT SUCCESSIVE OFFERING PERIODS UNLESS TERMINATED BY ME.

Dated:      _________________________

            _________________________________________
            Signature of Employee

            _________________________________________
            Spouse's Signature (If beneficiary under
            item 8 is OTHER than spouse)


                                       15
<PAGE>

                           [ARENA PHARMACEUTICALS LOGO]

                           ARENA PHARMACEUTICALS, INC.


                                    EXHIBIT B

                   2001 ARENA EMPLOYEE STOCK PURCHASE PLAN

                             *NOTICE OF WITHDRAWAL*


      The undersigned participant in the Offering Period of the 2001 Arena
Employee Stock Purchase Plan that began on ____________, 20____ (the
"Enrollment Date") hereby notifies the Company that he or she hereby
withdraws from the Offering Period. He or she hereby directs the Company to
pay to the undersigned as promptly as practicable all the payroll deductions
credited to his or her account with respect to such Offering Period. The
undersigned understands and agrees that his or her option for such Offering
Period will be automatically terminated. The undersigned understands further
that no further payroll deductions will be made for the purchase of shares in
the current Offering Period and the undersigned shall be eligible to
participate in succeeding Offering Periods only by delivering to the Company
a new Subscription Agreement.

                                       Name and Address of Participant:

                                       ________________________________________

                                       ________________________________________

                                       ________________________________________

                                       Signature:

                                       ________________________________________

                                       Date:___________________________________


                                       16