<PAGE>
Filed Pursuant to Rule 424(b)(3) and (c)
File Number 333-85339
PROSPECTUS SUPPLEMENT DATED NOVEMBER 1, 2000
to
Prospectus Dated November 12, 1999
and supplemented December 15, 1999, February 11, 2000,
April 26, 2000 and July 5, 2000
$345,000,000
IDEC PHARMACEUTICALS CORPORATION
LIQUID YIELD OPTION(TM) NOTES DUE 2019
(ZERO COUPON - SUBORDINATED)
AND
COMMON STOCK ISSUABLE UPON
CONVERSION OF THE LYONs
THIS PROSPECTUS SUPPLEMENT SUPPLEMENTS THE PROSPECTUS DATED
NOVEMBER 12, 1999 AND SUPPLEMENTED DECEMBER 15, 1999, FEBRUARY 11, 2000, APRIL
26, 2000 AND JULY 5, 2000 (THE "PROSPECTUS") OF IDEC PHARMACEUTICALS CORPORATION
("IDEC PHARMACEUTICALS" OR THE "COMPANY" OR "WE," "OUR" OR "US") RELATING TO THE
SALE BY CERTAIN OF OUR SECURITYHOLDERS OR BY THEIR PLEDGEES, DONEES, TRANSFEREES
OR OTHER SUCCESSORS IN INTEREST THAT RECEIVE ANY OF THESE SECURITIES AS A GIFT,
PARTNERSHIP DISTRIBUTION OR OTHER NON-SALE RELATED TRANSFER (THE "SELLING
SECURITYHOLDERS") OF UP TO $345,000,000 PRINCIPAL AMOUNT OF LIQUID YIELD
OPTION(TM) NOTES DUE 2019 (THE "LYONS") AND UP TO 4,646,460 SHARES OF COMMON
STOCK TO BE ISSUED UPON CONVERSION OF THE LYON, AS ADJUSTED TO REFLECT THE
TWO-FOR-ONE STOCK SPLIT OF THE COMPANY'S COMMON STOCK EFFECTED IN DECEMBER,
1999. YOU SHOULD READ THIS PROSPECTUS SUPPLEMENT IN CONJUNCTION WITH THE
PROSPECTUS, AND THIS PROSPECTUS SUPPLEMENT IS QUALIFIED BY REFERENCE TO THE
PROSPECTUS EXCEPT TO THE EXTENT THAT THE INFORMATION IN THIS PROSPECTUS
SUPPLEMENT SUPERSEDES THE INFORMATION CONTAINED IN THE PROSPECTUS. CAPITALIZED
TERMS USED IN THIS PROSPECTUS SUPPLEMENT AND NOT OTHERWISE DEFINED HEREIN HAVE
THE MEANINGS SPECIFIED IN THE PROSPECTUS.
SELLING SECURITYHOLDERS
The following table provides certain information with respect
to the principal amount of LYONs at maturity beneficially owned by an entity who
was identified in the prospectus as a Selling Securityholder and has increased
the principal amount of LYONs that may be offered by such Selling Securityholder
pursuant to the prospectus; the percentage of outstanding LYONs this represents;
and the number of shares of common stock issuable upon conversion of such LYONs
to be registered for sale hereby. Distributions may be made by certain of the
Selling Securityholders listed below to individuals other than those listed in
the prospectus. The table of Selling Securityholders in the prospectus is hereby
amended to amend the information provided for "Merrill Lynch Pierce Fenner &
Smith, Inc." and "All other Holders of LYONs or future transferee, pledgee,
donee or successor of any such Holders" in the table of Selling Securityholders
in the prospectus.
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<TABLE>
<CAPTION>
Aggregate Number of
Principal Amount Shares of
of LYONs at Percentage Common
Maturity That of LYONs Stock That
Name of Selling Securityholder May be Sold Outstanding May be Sold(1)
------------------------------ ---------------- ----------- --------------
<S> <C> <C> <C>
Merrill Lynch Pierce Fenner & Smith, Inc. $ 14,440,000 4.2% 194,477
All other Holders of LYONs or $ 11,255,000 3.3% 151,582
future transferee, pledgee, donee,
or successor of any such Holders.
</TABLE>
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(1) This prospectus supplement shall also cover any additional shares
of common stock which become issuable in connection with the shares registered
for sale hereby by reason of any stock dividend, stock split, recapitalization
or other similar transaction effected without the receipt of consideration which
results in an increase in the number of the Selling Securityholders' outstanding
shares of common stock. The number of shares of common stock listed in this
table have been adjusted to reflect the two-for-one stock split of the Company's
common stock effected in December, 1999.
(TM) Trademark of Merrill Lynch & Co.
