<PAGE>

                                                                     EXHIBIT 4.3

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



June 11, 2003                                                             Shares
                                                            --------------


      For Value Received, QUESTCOR PHARMACEUTICALS, INC., a California
corporation (the "Company"), with its principal office at 3260 Whipple Road,
Union City, California 94587, hereby certifies that [__] ("Holder"), or its
assigns, in partial consideration for Holder's purchase of Common Stock pursuant
to the Stock and Warrant Purchase Agreement dated June 11, 2003, by and among
the Company and the Purchasers who are signatories thereto (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 June
11, 2008 (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.

      Holder may purchase such number of shares of Common Stock at an exercise
price per share (as appropriately adjusted pursuant to Section 7 hereof) equal
to 125% of the Market Price, as such term is defined in the Purchase Agreement
(the "Exercise Price"). 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


                                       1
<PAGE>
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; provided that 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 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) Holder shall not, without obtaining the prior written consent of
the Company, which consent shall not be unreasonably withheld, assign its
interest in this Warrant in whole or in part to any person or persons. 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


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<PAGE>
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.

            (c) 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:

            (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.


                                       3
<PAGE>
            (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.

      SECTION 7. OFFICER'S CERTIFICATE. Whenever the Exercise Price shall be
adjusted as required by the provisions of Section 8, 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, unless at the time of exercise such
Warrant Shares are acquired pursuant to a registration statement that has been
declared effective under the Securities Act of


                                       4
<PAGE>
1933, as amended (the "Securities Act"), and applicable blue sky laws, 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
(except a new certificate for any Warrant Shares issued after the acquisition of
such Warrant Shares pursuant to a registration statement that has been declared
effective under the Securities Act) 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.

            (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) DISPOSITION OF HOLDER'S RIGHTS. In no event will Holder make a
disposition of any of its rights to acquire Common Stock, or of any Common Stock
issued upon exercise of such rights, unless and until (i) it shall have notified
the Company of the proposed disposition, and (ii) if requested by the Company,
it shall have furnished the Company with an


                                       5
<PAGE>
opinion of counsel (which counsel may either be inside or outside counsel to
Holder) satisfactory to the Company and its counsel to the effect that (A)
appropriate action necessary for compliance with the Securities Act has been
taken, or (B) an exemption from the registration requirements of the Securities
Act is available. Notwithstanding the foregoing, the restrictions imposed upon
the transferability of any of its rights to acquire Common Stock, or of any
Common Stock issued on the exercise of such rights do not apply to transfers
from the beneficial owner of any of the aforementioned securities to its nominee
or from such nominee to its beneficial owner, and shall terminate as to any
particular share of Common Stock when (1) such security shall have been
effectively registered under the Act and sold by the holder thereof in
accordance with such registration, (2) such security shall have been sold
without registration in compliance with Rule 144 under the Securities Act, or
(3) a letter shall have been issued to Holder at its request by the staff of the
Securities and Exchange Commission or a ruling shall have been issued to Holder
at its request by such Commission stating that no action shall be recommended by
such staff or taken by such Commission, as the case may be, if such security is
transferred without registration under the Securities Act in accordance with the
conditions set forth in such letter or ruling, and such letter or ruling
specifies that no subsequent restrictions on transfer are required. Whenever the
restrictions imposed hereunder shall terminate, as hereinabove provided, Holder
or a holder of a share of Common Stock then outstanding as to which such
restrictions have terminated shall be entitled to receive from the Company,
without expense to such holder, one or more new certificates for the Warrant or
for such shares of Common Stock not bearing any restrictive legend.

            (d) 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.

            (e) 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.

            (f) 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. REGISTRATION RIGHTS. The Warrant Shares issuable upon the
exercise of this Warrant are subject of certain registration rights granted by
the Company to the Holder as more specifically set forth in the Purchase
Agreement.

      SECTION 11. 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 12. 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


                                       6
<PAGE>
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 13. 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 14. 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.

      SECTION 15. 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 16. 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 17. 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 18. 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>
      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.

<TABLE>
<S>                                      <C>
                                         QUESTCOR PHARMACEUTICALS,  INC.

                                         By:
                                            -----------------------------------
                                            Name:
                                            Title:
</TABLE>


                                       8
<PAGE>
                                  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.

<TABLE>
<S>                                      <C>

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


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



                                         HOLDER:


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

                                         By:
                                            -----------------------------------

                                         Print Name:
                                                    ---------------------------

                                         Title:
                                               --------------------------------
</TABLE>


                                       9
<PAGE>
                                 ASSIGNMENT FORM

                                                        Dated            ,
                                                              -----------  ----


      FOR VALUE RECEIVED, ___________________ 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.

<TABLE>
<S>                                      <C>

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

                                         By:
                                            -----------------------------------

                                         Print Name:
                                                    ---------------------------

                                         Title:
                                               --------------------------------
</TABLE>


                                       10
<PAGE>
                                 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
                 ---------------------------------------------------------------

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

<TABLE>
<S>                                      <C>

                                         Dated
                                               --------------------------------

                                         Holder's Signature
                                                            -------------------

                                         Holder's Address
                                                         ----------------------
                                         --------------------------------------
</TABLE>

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.


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