<PAGE>
Filed Pursuant to Rule 424(b)(3) and (c)
File Number 333-85339
PROSPECTUS SUPPLEMENT DATED JULY 5, 2000
to
Prospectus Dated November 12, 1999
and supplemented December 15, 1999,
February 11, 2000 and April 26, 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 AND APRIL 26,
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
not identified in the prospectus as a Selling Securityholder; 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 include the entity who is
named below as a Selling Securityholder, and to amend the information provided
for "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>
Associated Electric & Gas Insurance $ 500,000 * 6,734
Services Limited
All other Holders of LYONs or $ 14,255,000 4.1% 191,986
future transferee, pledgee, donee,
or successor of any such Holders.
</TABLE>
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* Less than 1%.
(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.
