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                            STOCK PURCHASE AGREEMENT

     This Stock Purchase Agreement (the "Agreement") is made as of July 31,
2001 between Questcor Pharmaceuticals, Inc., a California corporation (the
"Company"), and Sigma-Tau Finance Holding S.A. (the "Purchaser").

     WHEREAS, the Company wishes to sell and the Purchaser desires to purchase
an aggregate of 5,279,034 newly authorized shares (the "Shares") of the
Company's Common Stock, no par value per share (the "Common Stock").

     NOW, THEREFORE, the parties hereto hereby agree as follows:

     1.   Purchase and Sale of the Shares.

               1.1  Aggregate Sale. Subject to the terms and conditions hereof,
the Company shall issue and sell to Purchaser an aggregate of 5,279,034 Shares
of Common Stock. The purchase price will be $0.663 per share, for an aggregate
purchase price of $3,500,000.

               1.2  Payment of Purchase Price. On or prior to the Closing Date
(as hereinafter defined), Purchaser will deliver to the Company $3,500,000 (the
"Purchase Price").

     2.   Closing Date and Delivery.

               2.1  Closing Date. The closing of the purchase and sale of the
Shares hereunder (the "Closing") will be held at such time (the "Closing Date")
as shall be agreed upon by the Company and the Purchaser and shall occur at the
offices of the Company, 3260 Whipple Road, Union City, CA 94587, but in no event
shall the Closing Date be later than August 6, 2001.

               2.2  Deliveries at Closing. At the Closing, the Company shall
deliver to the Purchaser a stock certificate registered in Purchaser's name
representing the Shares purchased by Purchaser. At the Closing, Purchaser shall
deliver to the Company proper payment of the Purchase Price in lawful money of
the United States of America in the form of a check or wire transfer of
immediately available funds. Purchaser's obligation to purchase the Shares shall
be subject to the following conditions:

                    (a)  the accuracy of the representations and warranties made
                         by the Company herein and the fulfillment of those
                         undertakings of the Company to be fulfilled prior to
                         Closing; and

                    delivery of the certificates representing the Shares.

The Company's obligation to sell the Shares shall be subject to the following
conditions:

                    (a)  the accuracy of the representations and warranties made
                         by Purchaser herein and the fulfillment of those
                         undertakings of Purchaser to be fulfilled prior to the
                         Closing; and

                    (b)  Purchaser's payment of the Purchase Price to the
                         Company.

     3.   Representations and Warranties by the Company. The Company represents
and warrants to and covenants and agrees with Purchaser that, except as set
forth in the Disclosure Schedule attached hereto as Schedule II (the "Disclosure
Schedule") or in the SEC Reports (as hereinafter defined):

               3.1  Organization and Standing. The Company is a corporation
duly organized, validly existing and in good standing under the laws of the
State of California, and has the requisite corporate power and authority to own,
lease and operate its properties and to carry on its business as now being
conducted. The Company is qualified


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to do business and is in good standing as a foreign corporation in every
jurisdiction in which the failure to so qualify would have a material adverse
effect on the financial condition or business of the Company.

     3.2 Changes. Except as set forth in the SEC Reports, since March 31, 2001,
the Company has not, to the extent material to the Company: (a) incurred any
debts, obligations or liabilities, absolute, accrued or contingent, whether due
or to become due, other than in the ordinary course of business; (b) mortgaged,
pledged or subjected to lien, charge, security interest or other encumbrance any
of its assets, tangible or intangible, other than in the ordinary course of
business; (c) waived any debt owed to the Company or its subsidiaries, other
than in the ordinary course of business; (d) satisfied or discharged any lien,
claim or encumbrance or paid any obligation other than in the ordinary course of
business; (e) declared or paid any dividends, other than in the ordinary course
of business; or (f) entered into any transaction other than in the usual and
ordinary course of business.

     3.3 Litigation. Except as set forth in the Disclosure Schedule or the SEC
Reports, there are no legal actions, suits, arbitrations or other legal,
administrative or governmental proceedings pending or, to the Company's
knowledge, threatened against the Company or its properties, assets or business,
and the Company is not aware of any facts which might result in or form the
basis for any such action, suit or other proceeding, in each case which, if
adversely determined, would individually or in the aggregate have a material
adverse effect on the financial condition or business of the Company.

     3.4 Compliance with Other Instruments. The execution and delivery of, and
the performance and compliance with, this Agreement and the transactions
contemplated hereby, with or without the giving of notice or passage of time,
will not (a) result in any breach of, or constitute a default under, or result
in the imposition of any lien or encumbrance upon any asset or property of the
Company pursuant to any agreement or other instrument to which the Company is a
party or by which it or any of its properties, assets or rights is bound or
affected, except for such matters which, either individually or in the
aggregate, would not have a material adverse effect on the financial condition
or business of the Company, (b) violate the Amended and Restated Articles of
Incorporation (the "Articles") or Bylaws (the "Bylaws") of the Company, or any
law, rule, regulation, judgment, order or decree; or (c) except for (i) the
listing of the Shares on the AMEX and such consents, approvals, authorizations,
registrations or qualifications as may be required under the Securities Exchange
Act of 1934, as amended (the "Exchange Act"), and (ii) applicable state
securities laws in connection with the purchase of the Shares by the Purchaser,
require any consent, approval, authorization or order of or filing with any
court or governmental agency or body, except for such matters which, either
individually or in the aggregate, would not have a material adverse effect on
the financial condition or business of the Company. The Company is not in
violation of its Articles or Bylaws nor in violation of, or in default under,
any lien, mortgage, lease, agreement or instrument, except for such defaults
which would not, individually or in the aggregate, have a material adverse
effect on the financial condition or business of the Company. The Company is not
subject to any restriction which would prohibit the Company from entering into
or performing its obligations under this Agreement, except for such restrictions
which would not, individually or in the aggregate, have a material adverse
effect on the ability of the Company to perform its obligations under this
Agreement.

     3.5 Reports and Financial Statements. As of their respective filing dates,
the Company's Amendment No. 1 to its Annual Report on Form 10-K for the fiscal
year ended December 31, 2000 filed on Form 10-K/A with the SEC on April 30,
2001, the Company's Proxy Statement in connection with the 2001 Annual Meeting
of Shareholders and all Forms 10-Q and 8-K filed by the Company with the
Securities and Exchange Commission (the "SEC") after December 31, 2000, in each
case without exhibits thereto (the "SEC Reports") were prepared in all material
respects in accordance with the requirements of the Securities Act of 1933 (the
"Securities Act") or the Exchange Act, as the case may be, and the rules and
regulations of the SEC thereunder applicable to such SEC Reports. The SEC
Reports, when read as a whole do not contain any untrue statements of a material
fact and do not omit to state a material fact necessary to make the statements
therein, in light of the circumstances under which they were made, not
misleading. The audited consolidated financial statements and unaudited interim
financial statements of the Company included in the SEC Reports have been
prepared in accordance with United States generally accepted accounting
principles applied on a consistent basis (except as may be indicated therein or
in the notes thereto) and fairly present, in all material respects, the
financial position of the Company as at the dates thereof and the results of its
operations and cash flows for the periods then ended subject, in the case of the
unaudited interim financial statements, to normal year-end adjustments and any
other adjustments described in such financial statements.


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     3.6 Shares.  The Shares, when issued and paid for pursuant to the terms of
this Agreement, will be duly and validly authorized, issued and outstanding,
fully paid, nonassessable and free and clear of all pledges, liens, encumbrances
and restrictions (other than arising under federal or state securities laws).
The issuance of the Shares is not subject to any preemptive or other similar
rights.

     3.7 Capital Stock.  As of June 30, 2001, 29,157,576 shares of the Common
Stock were issued and outstanding, 2,155,715 shares of the Company's Series A
Preferred Stock, no par value per share (the "Preferred Stock"), were issued and
outstanding, which are convertible into 2,155,715 shares of Common Stock, and
options and/or warrants to purchase 6,158,329 shares of Common Stock were issued
and outstanding. All of the outstanding shares of the Company's capital stock
are validly issued, fully paid and nonassessable. Except as set forth in this
Section 3.7, as of June 30, 2001, thee are no outstanding subscriptions,
options, warrants, calls, contracts, demands, commitments, conversion rights or
other agreements or arrangements of any character or nature whatever under which
the Company is or may be obligated to issue its Common Stock, Preferred Stock or
warrants or options to purchase the Common Stock or the Preferred Stock. No
holder of any security of the Company is entitled to any preemptive or similar
rights to purchase any securities of the Company.

     3.8 Corporate Acts and Proceedings.  This Agreement has been duly
authorized by the requisite corporate action and has been duly executed and
delivered by an authorized officer of the Company, and is a valid and binding
obligation of the Company, enforceable in accordance with its terms, except as
such enforceability may be limited by bankruptcy, insolvency, moratorium,
reorganization or other similar laws affecting the enforcement of creditors'
rights generally and as to limitations on the enforcement of the remedy of
specific performance and other equitable remedies. The requisite corporate
action necessary for the authorization, reservation, issuance and delivery of
the Shares has been taken by the Company.

     3.9 No Implied Representations.  All of the Company's representations and
warranties are contained in this Agreement, and no other representations or
warranties by the Company shall be implied.

     3.10 Filing of Reports.  Since the Company's Amendment No. 1 to its Annual
Report on Form 10-K for the fiscal year ended December 31, 2000 filed on Form
10-K/A with the SEC on April 30, 2001, the Company has filed with the SEC all
reports and other material required to be filed by it therewith pursuant to
Section 13, 14 or 15(d) of the Exchange Act.

     3.11 Compliance with Laws.  The business and operations of the Company have
been conducted in accordance with all applicable laws, rules and regulations of
all governmental authorities, except for such violations which would not,
individually or in the aggregate, have a material adverse effect on the
financial condition or business of the Company.

     3.12 Proprietary Rights.  To the knowledge of the Company, the Company owns
or is licensed to use all patents, patent applications, inventions, trademarks,
trade names, applications for registration of trademarks, service marks, service
mark applications, copyrights, trade secrets, licenses and rights in any thereof
and any other intangible property and assets (herein called the "Proprietary
Rights") which are material to the business of the Company. Except as would not
have a material adverse effect on the financial condition or business of the
Company, the Company does not have any knowledge of, and the Company has not
given or received any notice of, any pending conflicts with or infringement of
the rights of others with respect to any Proprietary Rights. Except as would not
have a material adverse effect on the financial condition or business of the
Company, no action, suit, arbitration, or legal, administrative or other
proceeding, or investigation is pending or, to the knowledge of the Company,
threatened, which involves any Proprietary Rights. Except as would not have a
material adverse effect on the financial condition or business of the Company,
to the knowledge of the Company, no Proprietary Rights used by the Company, and
no services or products sold by the Company, conflict with or infringe upon any
proprietary rights owned or licensed by any third party. Except as would not
have a material adverse effect on the financial condition or business of the
Company, no claims have been asserted by any person with respect to the validity
of the Company's ownership or right to use the Proprietary Rights and, to the
knowledge of the Company, there is no reasonable basis for any such claim to be
successful.

     3.13 Compliance with Environmental Laws.  Except as would not, singly or in
the aggregate, have a material adverse effect on the financial condition or
business of the Company, the Company is not in violation of



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any applicable statute, law or regulation relating to the environment or
occupational health and safety, and to the Company's knowledge, no expenditures
material to the Company are or will be required to comply with any such existing
statute, law or regulation. To the Company's knowledge, the Company does not
have any liability to any governmental authority or other third party arising
under or as a result of any past or existing statute, law or regulation, which
liability would be material to the Company.

          3.14  Permits, Licenses, Etc.  The Company owns, possesses or has
obtained, and is operating in compliance with, all governmental and
administrative licenses, permits, certificates, registrations, approvals,
consents and other authorizations (collectively, "Permits") necessary to own or
lease (as the case may be) and operate its properties, whether tangible or
intangible, and to conduct its businesses or operations as currently conducted,
except such licenses, permits, certificates, registrations, approvals, consents
and authorizations the failure of which to obtain would not have a material
adverse effect on the financial condition or business of the Company. The
Company has not received any notice of proceedings relating to the revocation,
modification or suspension of any Permits or any circumstance which would lead
it to believe that such proceedings are reasonably likely.

          3.15  Insurance.  The Company maintains insurance of the type and in
the amount which the Company believes is reasonably adequate for its business,
including, but not limited to, insurance covering all real and personal property
owned or leased by the Company against theft, damage, destruction, acts of
vandalism and all other risks customarily insured against by similarly situated
companies, all of which insurance is in full force and effect.

          3.16  Brokers or Finders.  No agent, broker, investment banker or
other person (as such term is defined in the Securities Act) is or will be
entitled to any broker's or finder's fee or any other commission or similar fee
from the Company in connection with any of the transactions contemplated hereby.

     4.   Representations and Warranties by the Purchaser; Restrictions on
Transfer and Future Purchases. Purchaser represents and warrants to, and
covenants and agrees with, the Company, as of the Closing Date, as follows:

          4.1  Authorization.  Purchaser has all requisite legal and corporate
or other power and capacity and has taken all requisite corporate or other
action to execute and deliver this Agreement, to purchase the Shares to be
purchased by it and to carry out and perform all of its obligations under this
Agreement. This Agreement constitutes the legal, valid and binding obligation of
Purchaser, enforceable in accordance with its terms, except as such
enforceability may be limited by bankruptcy, insolvency, moratorium,
reorganization or other similar laws affecting the enforcement of creditors'
rights generally and as to limitations on the enforcement of the remedy of
specific performance and other equitable remedies.

          4.2  Investor Status.  Purchaser is an "Accredited Investor" as
defined in Rule 501 of the Securities Act or a "Qualified Institutional Buyer,"
as such term is defined in Rule 144A of the Securities Act. Purchaser is aware
of the Company's business affairs and financial condition and has had access to
and has acquired sufficient information about the Company to reach an informed
and knowledgeable decision to acquire the Shares. Purchaser has such business
and financial experience as is required to give it the capacity to protect its
own interests in connection with the purchase of the Shares and is able to bear
the risks of an investment in the Shares. Purchaser is not itself a "broker" or
a "dealer" as defined in the Exchange Act and is not an "affiliate" of the
Company as defined in Rule 405 of the Securities Act.

          4.3  Investment Intent.  Purchaser is purchasing the Shares for its
own account as principal, for investment purposes only, and not with a present
view to or for resale, distribution or fractionalization thereof, in whole or in
part, within the meaning of the Securities Act. Purchaser understands that its
acquisition of the Shares have not been registered under the Securities Act or
registered or qualified under any state securities law in reliance on specific
exemptions therefrom, which exemptions may depend upon, among other things, the
bona fide nature of Purchaser's investment intent as expressed herein. Purchaser
has, in connection with its decision to purchase the number of Shares set forth
in this Agreement, relied solely upon the representations and warranties of the
Company contained herein. Purchaser will not, directly or indirectly, offer,
sell, pledge, transfer or otherwise dispose of (or

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solicit any offers to buy, purchase or otherwise acquire or take a pledge of
any of the Shares, except in compliance with the Securities Act and the rules
and regulations promulgated thereunder and all applicable state securities laws.

          4.4 Restricted Securities. Purchaser further acknowledges and
understands that the Shares may not be resold or otherwise transferred except
in a transaction registered under the Securities Act and applicable state
securities laws or an exemption therefrom, in each case as set forth in Section
5 below. Purchaser understands that until the Shares have been registered under
the Securities Act and all applicable state securities laws, the certificates
evidencing the Shares will be imprinted with a legend as provided in Section 5.

          4.5 No Legal, Tax Or Investment Advice. Purchaser understands that
nothing in this Agreement or any other materials presented to Purchaser in
connection with the purchase and sale of the Shares constitutes legal, tax or
investment advice. Purchaser has consulted such legal, tax and investment
advisors as it, its sole discretion, has deemed necessary or appropriate in
connection with its purchase of the Shares.

          4.6 Brokers or Finders. Upon the consummation of the transactions
contemplated by this Agreement, no agent, broker, investment banker or other
Person is or will be entitled to any broker's or finder's fee or any other
commission or similar fee from the Purchaser in connection with any of the
transactions contemplated hereby.

          4.7 Future Purchases. For a period of one year from the Closing Date,
Purchaser (on behalf of itself and its Affiliates) agrees not to purchase any
additional shares of Company Common Stock, or acquire beneficial ownership
thereof, not specifically contemplated by this Agreement, through the open
market or otherwise, unless first approved in writing by the Company's Board of
Directors.

     5. Restrictions on Transferability of Shares; Compliance with Securities
Act.

          5.1 Restrictive Legend. Each certificate representing the Shares
shall bear substantially the following legend (in addition to any legends
required under applicable state securities laws):

          THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED
          UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), OR UNDER
          THE SECURITIES LAWS OF ANY STATE. THESE SECURITIES ARE SUBJECT TO
          RESTRICTIONS ON TRANSFERABILITY AND RESALE AND MAY NOT BE TRANSFERRED
          OR RESOLD EXCEPT AS PERMITTED UNDER THE ACT AND THE APPLICABLE STATE
          SECURITIES LAWS, PURSUANT TO REGISTRATION OR EXEMPTION THEREFROM. THE
          ISSUER OF THESE SECURITIES MAY REQUIRE AN OPINION OF COUNSEL IN FORM
          AND SUBSTANCE SATISFACTORY TO THE ISSUER TO THE EFFECT THAT ANY
          PROPOSED TRANSFER OR RESALE IS IN COMPLIANCE WITH THE ACT AND ANY
          APPLICABLE STATE SECURITIES LAWS.

          5.2 Transfer of Shares. Purchaser hereby covenants with the Company
not to make any sale of the Shares except either (a) a sale of Shares in
accordance with Rule 144, in which case the Purchaser covenants to comply with
Rule 144 and to deliver such additional certificates and documents as the
Company may reasonably request, or (b) in accordance with another exemption
from the registration requirements of the Securities Act. Without limiting the
generality of the foregoing, it is understood that Purchaser and its Affiliates
may transfer the Shares to any other Affiliate; provided that such transfer is
in accordance with an exemption from the registration requirements of the
Securities Act. "Affiliate" shall mean (i) any corporation or business entity
50% or more of the capital or voting stock of which is owned directly or
indirectly by the Purchaser, Claudio Cavazza or Paolo Cavazza; (ii) any
corporation or business entity which directly or indirectly owns 50% or more of
the capital or voting stock of the Purchaser, or (iii) any corporation or
business entity under the direct or indirect control of such corporation or
business entity as described in (i) or (ii) above. The legend set forth in
Section 5.1 will be removed from a certificate representing Shares following
and in connection with any sale of Shares pursuant to subsection (a) hereof but
not in connection with any sale of Shares pursuant to subsection (b) hereof.


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     6.   Miscellaneous.

               6.1  Survival of Representations and Warranties. All
representations and warranties contained herein shall survive the execution and
delivery of this Agreement, any investigation at any time made by or on behalf
of the Purchaser, and the sale and purchase of the Shares and payment therefor.

               6.2  Entire Agreement. This Agreement contains the entire
agreement between the parties with respect to the subject matter hereof and
supersedes all prior and contemporaneous arrangements or understandings with
respect thereto.

               6.3  Headings. The headings of the sections of this Agreement
have been inserted for convenience of reference only and do not constitute a
part of this Agreement.

               6.4  Choice of Law. It is the intention of the parties that the
internal laws of the State of California, without regard to the body of law
controlling conflicts of law, shall govern the validity of this Agreement, the
construction of its terms and the interpretation of the rights and duties of the
parties set forth herein.

               6.5  Counterparts. This Agreement may be executed concurrently in
two or more counterparts, each of which shall be deemed an original, but all of
which together shall constitute one and the same instrument.

               6.6  Assignment; Parties in Interest. This Agreement may not be
pledged, assigned or otherwise transferred by the Purchaser except by operation
of law but all the terms and provision of this Agreement shall be binding upon
and inure to the benefit of and be enforced by the successors in interest of the
parties hereto.

               6.7  Amendments. No amendment, modification, waiver, discharge or
termination of any provision of this Agreement nor consent to any departure by
the Purchaser or the Company therefrom shall in any event be effective unless
the same shall be in writing and signed by the party to be charged with
enforcement, and then shall be effective only in the specific instance and for
the purpose for which given. No course of dealing between the parties hereto
shall operate as an amendment of, or a waiver of any right under, this
Agreement.

               6.8  Severability. Whenever possible, each provision of this
Agreement shall be interpreted in such manner as to be effective and valid, but
if any provision of this Agreement is held to be invalid or unenforceable in any
respect, such invalidity or unenforceability shall not render invalid or
unenforceable any other provision of this Agreement.

               6.9  Notices. All notices, requests, consents and other
communications hereunder to any party shall be deemed to be sufficient if
contained in a written instrument delivered in person or sent by telecopy,
nationally recognized overnight courier or first class registered or certified
mail, return receipt requested, postage prepaid, addressed to such party at the
address set forth below or such other address as may hereafter be designated in
writing by such party to the other party:

                         If to the Company, to:
                         Questcor Pharmaceuticals, Inc.
                         3260 Whipple Road
                         Union City, California 94587
                         Attn: Charles J. Casamento

                         With a copy to:
                         Latham & Watkins
                         701 "B" Street, Suite 2100
                         San Diego, California 92101
                         Attn: David A. Hahn, Esq.




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               If to the Purchaser, to:
               Sigma-Tau Finance Holding S.A.
               administrative office: 19-21 Bd. du Prince Henri
               L-1724 Luxembourg
               LUXEMBOURG
               Attn: Mr. Antonio Nicolai/Mr. Massimo Longoni

               With a copy to:
               Cahill Gordon & Reindel
               80 Pine Street
               New York, New York 10005
               Attn: John Mitchell, Esq.

                            [SIGNATURE PAGES FOLLOW]


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     IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed and delivered by their proper and duly authorized representatives as of
the day and year first above written.

                                        Questcor Pharmaceuticals, Inc.

                                        By: /s/ CHARLES J. CASAMENTO
                                            ----------------------------

                                        Name: Charles J. Casamento
                                             ---------------------------

                                        Title: Chairman, President & CEO
                                              --------------------------


                                        Sigma-Tau Finance Holding S.A.

                                        By: /s/ GERMAIN BIRGEN
                                           -----------------------------

                                        Name: Germain Birgen
                                             ---------------------------

                                        Title: Director
                                              --------------------------







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