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                                                                    EXHIBIT 10.7

                      STOCK AND WARRANT PURCHASE AGREEMENT

        This Stock and Warrant Purchase Agreement (the "Agreement") is made as
of April 5, 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 2,873,563 newly authorized shares (the "Shares") of the
Company's Common Stock, no par value per share (the "Common Stock"), and one (1)
warrant to purchase an additional 2,873,563 shares of Common Stock (the
"Warrant").

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

        1. Purchase and Sale of Shares and Warrant.

            1.1 Aggregate Sale. Subject to the terms and conditions hereof, the
Company shall issue and sell to Purchaser an aggregate of 2,873,563 Shares of
Common Stock. The purchase price will be $0.522 per share, for an aggregate
purchase price of $1,499,999.80. The Company shall sell a Warrant to Purchaser
to purchase an additional 2,873,563 shares of the Company's Common Stock. The
purchase price of such Warrant shall be $100,000. The shares of Common Stock
issuable upon the exercise of the Warrant (the "Warrant Shares") shall have an
exercise price equal to $0.522 per share and shall be exercisable from the date
of issuance until the close of business on September 29, 2001, and shall be
subject to the other terms and conditions set forth in the Warrant.

            1.2 Payment of Purchase Price. On or prior to the Closing Date (as
hereinafter defined), Purchaser will deliver to Company $1,599,999.80 (the
"Total Purchase Price"), which represents the aggregate purchase price of
$1,499,999.80 for the purchase of the Shares plus the aggregate purchase price
of $100,000 for the purchase of the Warrant.

            1.3 Warrant Credit. The $100,000 to be paid by Purchaser for the
Warrant shall be non-refundable, and in the event that Purchaser elects not to
exercise such Warrant in full on or before the close of business on September
29, 2001 (the "Expiration Date"), Company shall have no obligation to return any
such portion of the $100,000 paid for the Warrant. In the event that Purchaser
exercises such Warrant in full, on or before the Expiration Date, the $100,000
paid for the Warrant will be credited toward the purchase of the aggregate of
2,873,563 shares of Company Common Stock under the Warrant.

        2. Closing Date and Delivery.

            2.1 Closing Date. The closing of the purchase and sale of the Shares
and Warrant 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, 26118 Research Road, Hayward, CA 94545, but in no
event shall the Closing Date be later than April 5, 2001.

            2.2 Deliveries at Closing. At the Closing, the Company shall deliver
the following to Purchaser: (a) a stock certificate registered in Purchaser's
name representing the Shares purchased by Purchaser; and (b) a Warrant in
Purchaser's name. At the Closing, Purchaser shall deliver to the Company proper
payment of the Total 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 and Warrant 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

                  (b) delivery of the certificates representing the Shares and
                      the Warrant.

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

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                  (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 Total 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 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 September
30, 2000, 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 Warrant and
the transactions contemplated hereby or thereby, 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 and the Warrant 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"), (ii) the receipt of any shareholder approvals necessary for the exercise
of the warrant in full by Purchaser to be in compliance with the rules and
regulations of the AMEX, and (iii) applicable state securities laws in
connection with the purchase of the Shares and the Warrant 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 or the Warrant, 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 and the Warrant.

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            3.5 Reports and Financial Statements. As of their respective filing
dates, the Company's Form 10-K for the year ended December 31, 1999, the
Company's Proxy Statement in connection with the 1999 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 January 1, 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.

            3.6 Shares. The Shares, the Warrant and the Warrant Shares, when
issued and paid for pursuant to the terms of this Agreement or the Warrant, as
applicable, 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, the Warrant and the Warrant Shares is not subject to any
preemptive or other similar rights. The Company has duly reserved 2,873,563
shares of its authorized but unissued Common Stock for issuance upon exercise of
the Warrant by the Purchaser, and such shares shall remain so reserved (subject
to reduction from time to time for Common Stock issued upon the exercise of the
Warrant), as long as the Warrant is exercisable.

            3.7 Capital Stock. As of November 10, 2000, 25,265,862 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 7,723,862 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 November 10, 2000, there 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, the Warrant and the Warrant Shares has been taken by the Company.
Upon execution and delivery thereof by a duly authorized officer of the Company,
the Warrant will be valid and binding obligations of the Company, enforceable in
accordance with their 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.

            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 Annual Report on Form
10-K for the fiscal year ended December 31, 1999, 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. The Company has filed a Form
12b-25 and has received an extension for filing its Annual Report on Form 10-K
for the fiscal year ended December 31, 2000.

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            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 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 such 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.

            3.17 Shareholder Approval. The Company shall use its reasonable best
efforts to obtain shareholder approval necessary for the exercise of the warrant
in full by Purchaser to be in compliance with the rules and regulations of the
AMEX.

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        4. Representations and Warranties by the Purchasers; Restrictions on
Transfer. 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 and the
Warrant 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 and the Warrant. 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
Warrant and is able to bear the risks of an investment in the Shares and the
Warrant. 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 and the
Warrant 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 and the Warrant has 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 and the Warrant 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 solicit any offers to buy, purchase
or otherwise acquire or take a pledge of) any of the Shares or the Warrant,
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, the Warrant and the Warrant 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, the Warrant and the Warrant Shares have been registered under the
Securities Act and all applicable state securities laws, the certificates
evidencing the Shares, the Warrant and the Warrant 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 and the Warrant 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 and the Warrant.

            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.

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

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

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            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 and Warrant. Purchaser hereby covenants with
the Company not to make any sale of the Shares or Warrant Shares except either
(a) a sale of Shares or Warrant 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 and/or the
Warrant 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 or the Warrant Shares, as the case may be,
following and in connection with any sale of Shares or Warrant Shares pursuant
to subsection (a) hereof but not in connection with any sale of Shares or
Warrant Shares pursuant to subsection (b) hereof.

        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 the Warrant 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

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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.
                             26118 Research Road Hayward,
                             California 94545
                             Attn: Hans P. Schmid

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

                             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, and CEO

                                        Sigma-Tau Finance Holding S.A.

                                               /s/ PATRICK EHRHARDT
                                                    and
                                        By:    /s/ MARYSE SANTINI
                                               ---------------------------------
                                        Name:   Patrick Ehrhardt
                                                    and
                                                Maryse Santini

                                        Title:  Directors

                                       8<PAGE>   1
                                                                    EXHIBIT 10.8

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.

                         QUESTCOR PHARMACEUTICALS, INC.

               WARRANT FOR THE PURCHASE OF SHARES OF COMMON STOCK

April 5, 2001                                                   2,873,563 Shares

For Value Received, QUESTCOR PHARMACEUTICALS, INC., a California corporation
(the "Company"), with its principal office at 26118 Research Road, Hayward,
California 94545, hereby certifies that Sigma-Tau Finance Holding S.A.
("Holder"), or its assigns, in consideration of payment to the Company of
$100,000 and for Holder's purchase of Common Stock pursuant to the Stock and
Warrant Purchase Agreement dated April 5, 2001, by and among the Company and the
Purchaser (the "Purchase Agreement"), is entitled, subject to the provisions of
this Warrant, to purchase from the Company, at any time before 5:00 p.m.
(Pacific Standard Time) on September 29, 2001 (the "Expiration Date"), the
number of fully paid and nonassessable shares of Common Stock of the Company set
forth above, subject to adjustment as hereinafter provided. In the event Holder
exercises this Warrant in full, on or before such Expiration Date, the $100,000
paid for the Warrant will be credited toward the purchase of the aggregate of
2,873,563 shares of Company Common Stock, provided, that if the Company has not
received the shareholder approval contemplated by the last sentence of the
following paragraph, the $100,000 shall be credited toward the purchase of
2,161,752 shares (subject to adjustments for stock-splits, dividends, etc.)

        Holder may purchase such number of shares of Common Stock up to the
number set forth above at an exercise price per share (as appropriately adjusted
pursuant to Section 6 hereof) equal to $0.522 (the "Exercise Price").
Notwithstanding the foregoing, however, Holder shall not exercise this Warrant
for greater than 2,161,752 shares (subject to adjustments for stock-splits,
dividends, etc.), unless the Company has received shareholder approval in
compliance with the rules and regulations of the American Stock Exchange.

                                       1
<PAGE>   2
        The term "Common Stock" shall mean the aforementioned Common Stock of
the Company, together with any other equity securities that may be issued by the
Company in addition thereto or in substitution therefor as provided herein. The
number of shares of Common Stock to be received upon the exercise of this
Warrant and the price to be paid for a share of Common Stock are subject to
adjustment from time to time as hereinafter set forth. The shares of Common
Stock deliverable upon such exercise, as adjusted from time to time, are
hereinafter sometimes referred to as "Warrant Shares."

        SECTION 1. EXERCISE OF WARRANT. This Warrant may be exercised in whole
or in part on any business day prior to the Expiration Date by presentation and
surrender hereof to the Company at its principal office at the address set forth
in the initial paragraph hereof (or at such other address as the Company may
hereafter notify Holder in writing) with the Purchase Form annexed hereto duly
executed and accompanied by proper payment of the Exercise Price in lawful money
of the United States of America in the form of a check or wire transfer of
immediately available funds, subject to collection, for the number of Warrant
Shares specified in the Purchase Form. If this Warrant should be exercised in
part only, the Company shall, upon surrender of this Warrant, execute and
deliver a new Warrant evidencing the rights of Holder thereof to purchase the
balance of the Warrant Shares purchasable hereunder. Upon receipt by the Company
of this Warrant and such Purchase Form, together with proper payment of the
Exercise Price, at the principal office of the Company, Holder shall be deemed
to be the holder of record of the Warrant Shares, notwithstanding that the stock
transfer books of the Company shall then be closed or that certificates
representing such Warrant Shares shall not then be actually delivered to Holder.

        SECTION 2. RESERVATION OF SHARES. The Company hereby agrees that at all
times there shall be reserved for issuance and delivery upon exercise of this
Warrant all shares of its Common Stock or other shares of capital stock of the
Company from time to time issuable upon exercise of this Warrant. All such
shares shall be duly authorized and, when issued upon such exercise in
accordance with the terms of this Warrant, shall be validly issued, fully paid
and nonassessable.

        SECTION 3. FRACTIONAL INTEREST. The Company will not issue a fractional
share of Common Stock upon exercise of this Warrant. Instead, the Company will
deliver its check for the current market value of the fractional share. The
current market value of a fraction of a share is determined as follows: multiply
the current market price of a full share by the fraction of a share and round
the result to the nearest cent.

        SECTION 4. TRANSFERS; ASSIGNMENT OR LOSS OF WARRANT.

               (a) Subject to the terms and conditions contained in Section 9
hereof, this Warrant and all rights hereunder are transferable in whole or in
part by Holder and any successor transferee. Notwithstanding the foregoing
sentence, except in the case of a transfer pursuant to Section 4(b), prior to
such transfer Holder shall give thirty (30) days prior written notice of any
such transfer to the Company, and the Company shall have the right to acquire
the Warrant under the identical provisions contained in such notice by giving
Holder written notice within fifteen (15) days of receipt of such notice. The
Company's failure to respond to said notice within said

                                       2
<PAGE>   3
fifteen (15) days shall be deemed a waiver of this right of first refusal. The
transfer shall be recorded on the books of the Company upon receipt by the
Company of the Transfer Notice annexed hereto, at its principal offices and the
payment to the Company of all transfer taxes and other governmental charges
imposed on such transfer.

               (b) Without limiting the generality of the first sentence of
clause (a) above, it is understood that Holder and its Affiliates may transfer
the Shares and/or the Warrant 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 Holder, 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 Holder, 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.

               (c) Subject to the provisions of Section 9, upon surrender of
this Warrant to the Company or at the office of its stock transfer agent or
warrant agent, with the Assignment Form annexed hereto duly executed and funds
sufficient to pay any transfer tax, the Company shall, without charge, execute
and deliver a new Warrant or Warrants in the name of the assignee or assignees
named in such instrument of assignment (any such assignee will then be a
"Holder" for purposes of this Warrant) and, if Holder's entire interest is not
being assigned, in the name of Holder, and this Warrant shall promptly be
canceled.

               (d) Upon receipt of evidence satisfactory to the Company of the
loss, theft, destruction or mutilation of this Warrant, and (in the case of
loss, theft or destruction) of indemnification satisfactory to the Company, and
upon surrender and cancellation of this Warrant, if mutilated, the Company shall
execute and deliver a new Warrant of like tenor and date. In the event that this
Warrant is lost, stolen, destroyed or mutilated, Holder shall pay all reasonable
attorneys' fees and expenses incurred by the Company in connection with the
replacement of this Warrant and the issuance of a new Warrant.

        SECTION 5. RIGHTS OF HOLDER. Holder shall not, by virtue hereof, be
entitled to any rights of a stockholder in the Company, either at law or equity,
and the rights of Holder are limited to those expressed in this Warrant. Nothing
contained in this Warrant shall be construed as conferring upon Holder hereof
the right to vote or to consent or to receive notice as a stockholder of the
Company on any matters or with respect to any rights whatsoever as a stockholder
of the Company. No dividends or interest shall be payable or accrued in respect
of this Warrant or the interest represented hereby or the Warrant Shares
purchasable hereunder until, and only to the extent that, this Warrant shall
have been exercised in accordance with its terms.

        SECTION 6. ADJUSTMENT OF EXERCISE PRICE AND NUMBER OF SHARES. The number
and kind of securities purchasable upon the exercise of the Warrant and the
Exercise Price shall be subject to adjustment from time to time upon the
occurrence of certain events, as follows:

                                       3
<PAGE>   4
               (a) RECLASSIFICATION OF OUTSTANDING SECURITIES. In case of any
reclassification, change or conversion of securities of the class issuable upon
exercise of this Warrant (other than a change in par value, or from par value to
no par value, or from no par value to par value, or as a result of a subdivision
or combination), the Company shall execute a new Warrant (in form and substance
reasonably satisfactory to the Holder of this Warrant) providing that the Holder
of this Warrant shall have the right to exercise such new Warrant and upon such
exercise to receive, in lieu of each share of Common Stock theretofore issuable
upon exercise of this Warrant, the kind and amount of shares of stock, other
securities, money and property receivable upon such reclassification or change
by a holder of one share of Common Stock. Such new Warrant shall provide for
adjustments that shall be as nearly equivalent as may be practicable to the
adjustments provided for in this Section 6. The provisions of this subsection
(a) shall similarly apply to successive reclassification or changes.

               (b) SUBDIVISIONS OR COMBINATION OF SHARES. If the Company at any
time while this Warrant remains outstanding and unexpired shall subdivide or
combine its Common Stock, the Exercise Price and the number of Warrant Shares
issuable upon exercise hereof shall be proportionately adjusted.

               (c) STOCK DIVIDENDS. If the Company at any time while this
Warrant is outstanding and unexpired shall pay a dividend payable in shares of
Common Stock (except any distribution specifically provided for in the foregoing
subsections (a) and (b)), then the Exercise Price shall be adjusted, from and
after the date of determination of shareholders entitled to receive such
dividend or distribution, to that price determined by multiplying the Exercise
Price in effect immediately prior to such date of determination by a fraction
(a) the numerator of which shall be the total number of shares of Common Stock
outstanding immediately prior to such dividend or distribution, and (b) the
denominator of which shall be the total number of shares of Common Stock
outstanding immediately after such dividend or distribution, and the number of
Warrant Shares subject to this Warrant shall be proportionately adjusted.

               (d) NOTICE OF RECORD DATE. In the event of any taking by the
Company of a record of its shareholders for the purpose of determining
shareholders who are entitled to receive payment of any dividend (other than a
cash dividend) or other distribution, any right to subscribe for, purchase or
otherwise acquire any share of any class or any other securities or property, or
to receive any other right, or for the purpose of determining shareholders who
are entitled to vote in connection with any proposed merger or consolidation of
the Company with or into any other corporation, or any proposed sale, lease or
conveyance of all or substantially all of the assets of the Company, or any
proposed liquidation, dissolution or winding up of the Company, the Company
shall mail to the Holder of this Warrant, at least ten days prior to the date
specified therein, a notice specifying the date on which any such record is to
be taken for the purpose of such dividend, distribution or right, and the amount
and character of such dividend, distribution or right.

               (e) NO ADJUSTMENT UPON EXERCISE OF WARRANTS. No adjustments shall
be made under any Section herein in connection with the issuance of Warrant
Shares upon exercise of the Warrants.

                                       4
<PAGE>   5
        SECTION 7. OFFICER'S CERTIFICATE. Whenever the Exercise Price shall be
adjusted as required by the provisions of Section 6, the Company shall deliver
an officer's certificate showing the adjusted Exercise Price determined as
herein provided, setting forth in reasonable detail the facts requiring such
adjustment and the manner of computing such adjustment. Each such officer's
certificate shall be signed by the chairman, president or chief financial
officer of the Company.

        SECTION 8. TRANSFER TO COMPLY WITH THE SECURITIES ACT OF 1933. This
Warrant may not be exercised and neither this Warrant nor any of the Warrant
Shares, nor any interest in either, may be offered, sold, assigned, pledged,
hypothecated, encumbered or in any other manner transferred or disposed of, in
whole or in part, except in compliance with applicable United States federal and
state securities or blue sky laws and the terms and conditions hereof. Each
Warrant shall bear a legend in substantially the same form as the legend set
forth on the first page of this Warrant. Each certificate for Warrant Shares
issued upon exercise of this Warrant shall bear a legend substantially in the
following form:

        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.

Any certificate for any Warrant Shares issued at any time in exchange or
substitution for any certificate for any Warrant Shares bearing such legend
shall also bear such legend unless, in the opinion of counsel for the Company,
the Warrant Shares represented thereby need no longer be subject to the
restriction contained herein. The provisions of this Section 8 shall be binding
upon all subsequent holders of certificates for Warrant Shares bearing the above
legend and all subsequent holders of this Warrant, if any.

        SECTION 9. REPRESENTATIONS AND COVENANTS OF HOLDER. This Warrant has
been entered into by the Company in reliance upon the following representations
and covenants of Holder, which by its execution hereof Holder hereby confirms:

               (a) INVESTMENT PURPOSE. The right to acquire Common Stock, and
any Common Stock issued upon exercise of Holder's rights contained herein, will
be acquired for investment and not with a view to the sale or distribution of
any part thereof, and Holder has no present intention of selling or engaging in
any public distribution of the same except pursuant to a registration or
exemption.

                                       5
<PAGE>   6
               (b) PRIVATE ISSUE. Holder understands (i) that the Common Stock
issuable upon exercise of Holder's rights contained herein is not registered
under the Securities Act or qualified under applicable state securities laws on
the ground that the issuance contemplated by this Warrant will be exempt from
the registration and qualification requirements thereof, and (ii) that the
Company's reliance on such exemption is predicated on the representations set
forth in this Section 9.

               (c) FINANCIAL RISK. Holder has such knowledge and experience in
financial and business matters as to be capable of evaluating the merits and
risks of its investment and has the ability to bear the economic risks of its
investment.

               (d) RULE 144. Holder also understands that any sale of its rights
to purchase Common Stock, or of any Common Stock, which might be made by it in
reliance upon Rule 144 under the Securities Act may be made only in accordance
with the terms and conditions of that Rule.

               (e) ACCREDITED INVESTOR. Holder is an "accredited investor"
within the meaning of the Securities Act Rule 501 of Regulation D, as presently
in effect.

        SECTION 10. SATURDAYS, SUNDAYS AND HOLIDAYS. If the last or appointed
day for the taking of any action or the expiration of any right required or
granted herein shall be a Saturday or a Sunday or shall be a legal holiday in
the State of California, then such action may be taken or such right may be
exercised on the next succeeding day not a Saturday, Sunday or legal holiday in
the State of California.

        SECTION 11. ISSUE TAX. The issuance of certificates for Common Stock
upon the exercise of the Warrant shall be made without charge to the holder of
the Warrant for any issue tax (other than any applicable income taxes) in
respect thereof; provided, however, that the Company shall not be required to
pay any tax which may be payable in respect of any transfer involved in the
issuance and delivery of any certificates in a name other than that of the then
Holder of the Warrant being exercised.

        SECTION 12. MODIFICATION AND WAIVER. Neither this Warrant nor any term
hereof may be changed, waived, discharged or terminated other than by an
instrument in writing signed by the Company and by Holder.

        SECTION 13. NOTICES. Unless otherwise specified herein, any notice,
request or other document required or permitted to be given or delivered to
Holder or the Company shall be given in writing and shall be deemed effectively
given (i) upon personal delivery to the party to be notified, (ii) three (3)
days after deposit in the United States mail if sent by registered or certified
mail, postage prepaid, or (iii) one (1) day after deposit with an overnight
courier, specifying next day delivery, with written verification of receipt. All
communications shall be sent to Holder at its address as shown on the books of
the Company, or to the Company at the address indicated therefor in the first
paragraph of this Warrant.

                                       6
<PAGE>   7
        SECTION 14. DESCRIPTIVE HEADINGS AND GOVERNING LAW. The description
headings of the several sections and paragraphs of this Warrant are inserted for
convenience only and do not constitute a part of this Warrant. This Warrant
shall be construed and enforced in accordance with, and the rights of the
parties shall be governed by, the laws of the State of California, without
regard to its conflicts of laws principles.

        SECTION 15. ATTORNEYS' FEES. In any litigation, arbitration or court
proceeding between the Company and Holder relating hereto, the prevailing party
shall be entitled to attorneys' fees and expenses and all costs of proceedings
incurred in enforcing this Warrant.

        SECTION 16. SURVIVAL. The representations, warranties, covenants and
conditions of the respective parties contained herein or made pursuant to this
Warrant shall survive the execution and delivery of this Warrant.

        SECTION 17. SEVERABILITY. In the event any one or more of the provisions
of this Warrant shall for any reason be held invalid, illegal or unenforceable,
the remaining provisions of this Warrant shall be unimpaired, and the invalid,
illegal or unenforceable provision shall be replaced by a mutually acceptable
valid, legal and enforceable provision, which comes closest to the intention of
the parties underlying the invalid, illegal or unenforceable provision.

                            [Signature Page Follows]

                                       7
<PAGE>   8
        IN WITNESS WHEREOF, the Company has duly caused this Warrant to be
signed by its duly authorized officer and to be dated as of the date first above
written.

                                       COMPANY:

                                       QUESTCOR PHARMACEUTICALS,  INC.

                                       By: /s/ CHARLES J. CASAMENTO
                                           -------------------------------------
                                           Charles J. Casamento
                                           Chief Executive Officer

                                       8
<PAGE>   9
                                  PURCHASE FORM

                                                         Dated ___________, ____

        The undersigned hereby irrevocably elects to exercise the within Warrant
to purchase ______ shares of Common Stock and hereby makes payment of
$_____________ in payment of the exercise price thereof, together with all
applicable transfer taxes, if any.

        In exercising its rights to purchase the Common Stock of Questcor
Pharmaceuticals, Inc., the undersigned hereby confirms and acknowledges the
investment representations and warranties made in Section 9 of the Warrant.

        Please issue a certificate or certificates representing said shares of
Common Stock in the name of the undersigned or in such other name as is
specified below.

                                       -----------------------------------------
                                       (Name)

                                       -----------------------------------------
                                       (Address)

                                       -----------------------------------------

                                       HOLDER:

                                       SIGMA-TAU FINANCE HOLDING S.A.

                                       By:
                                          --------------------------------------
                                       Print Name:
                                                   -----------------------------
                                       Title:
                                               ---------------------------------

                                       9
<PAGE>   10
                                 ASSIGNMENT FORM

                                                          Dated _________, _____

        FOR VALUE RECEIVED, Sigma-Tau Finance Holding S.A. hereby sells, assigns
and transfers unto _________________________________________________ (the
"Assignee"),           (please type or print in block letters)
________________________________________________________________________________
                                (insert address)
its right to purchase up to __________shares of Common Stock represented by this
Warrant and does hereby irrevocably constitute and appoint _____________________
attorney, to transfer the same on the books of the Company, with full power of
substitution in the premises.

                                       SIGMA-TAU FINANCE HOLDING S.A.

                                       By:
                                          --------------------------------------
                                       Print Name:
                                                   -----------------------------
                                       Title:
                                               ---------------------------------

                                       10
<PAGE>   11
                                 TRANSFER NOTICE

        (To transfer or assign the foregoing Warrant, execute this form and
        supply required information. Do not use this form to purchase shares.)

        FOR VALUE RECEIVED, the foregoing Warrant and all rights evidenced
thereby are hereby transferred and assigned to:

--------------------------------------------------------------------------------
                                 (Please Print)

whose address is
                 ---------------------------------------------------------------

--------------------------------------------------------------------------------

                                       Dated
                                             -----------------------------------
                                       Holder's Signature
                                                          ----------------------
                                       Holder's Address
                                                         -----------------------

Note:     The signature to this Transfer Notice must correspond with the name as
          it appears on the face of the Warrant, without alteration or
          enlargement or any change whatever. Officers of corporations and those
          acting in a fiduciary or other representative capacity should file
          proper evidence of authority to assign the foregoing Warrant.

                                       11

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