Exhibit 10.37

AMENDMENT TO
QUESTCOR PHARMACEUTICALS, INC.
8% DEBENTURE

     This Amendment (the “Amendment”) to the 8% Convertible Debenture (the
“Debenture”) dated March 15, 2002 issued by Questcor Pharmaceuticals, Inc., a
California corporation (the “Company”), in favor of SF Capital Partners Ltd.
(the “Holder”) is made and entered into as of March 10, 2005. The Company and
Holder desire to amend the Debenture as set forth below.

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein, the parties hereby agree to amend the Debenture as follows:

     1. Capitalized terms not otherwise defined herein will have the meanings
set forth in the Debenture.

     2. The parties hereby agree that the Maturity Date of the Debenture is
extended until April 15, 2005.

     3. The notice dated February 14, 2005 from the Company to the Holder of the
Company’s election to repay the Debenture by delivering shares of Common Stock
to Holder is hereby rescinded and shall be of no further force or effect.

     4. Section 5(c) of the Debenture is hereby amended to read in its entirety
as follows:

          (c) Payment in Shares. At the Company’s option, it may repay all or
any portion of the Debenture at the Maturity Date by delivering freely
tradeable, registered shares of its Common Stock to Holder; provided that (i) it
delivers irrevocable, written notice of such election to Holder by the close of
business on April 1, 2005 and such notice specifies the amount of the debenture
to be repaid in shares of Common Stock and (ii) all Equity Conditions have been
satisfied. For the purposes of repayment of the Debenture in shares of Common
Stock, such shares shall be valued at the lower of (x) 90% of the average of the
Closing Price for the twenty (20) Trading Days prior to the Maturity Date and
(y) 90% of the average of the Closing Price for the twenty (20) Trading Days
prior to March 15, 2005. Such shares shall be delivered to Holder within at
least three (3) days of the Maturity Date via the Depository Trust Corporation
DWAC System; provided that any cash repayment shall be due and payable on the
Maturity Date.

     5. This Amendment shall be effective as of the date hereof. The Debenture,
as amended by this Amendment, shall remain in full force and effect.

     IN WITNESS WHEREOF, the parties have executed this Amendment as of the date
first written above.

              SF CAPITAL PARTNERS LTD.   QUESTCOR PHARMACEUTICALS, INC.
 
            /s/ BRIAN H. DAVIDSON   /s/ JAMES L. FARES      
By:
  Brian H. Davidson   By:   James L. Fares
Title:
  Authorized Signatory   Title:   President & CEO