Icahn's affiliated entity, High River Limited Partnership, will nominate four members to Forest's nine-member board at the company's 2011 annual meeting. Forest said it has been informed that Icahn-related entities own about 6.5 percent of Forest's outstanding shares.

The move by Icahn appears to be his latest activist salvo in the healthcare industry, following agitation at Genzyme Corp. and Biogen Idec Inc., among other companies.

"While we have not yet had a chance to meet with Mr. Icahn to discuss his ideas for the company, we welcome constructive input from all of our shareholders," Forest Chief Executive Officer Howard Solomon said in a statement.

Icahn's nominees are Alexander Denner, Richard Mulligan, Lucian Bebchuk and Eric Ende.

Icahn representatives were not immediately available for a comment.

Forest, with a market value of about $11 billion, faces an impending sales hit early next year from the U.S. patent expiration of its top-selling drug, the antidepressant Lexapro, which represents more than half of the company's annual revenue.

Another major product, Alzheimer's medicine Namenda, also is expected to lose patent protection in the coming years.

Forest has been trying to acquire companies and licensing product rights to make up for those declines and spur future growth. It recently acquired Clinical Data Inc. for $1.2 billion to get access to the newly approved Viibryd antidepressant.

In April, Forest projected that earnings would not slump as Wall Street had feared after its Lexapro patent lapses and cheap generics flood the market.

"We are very excited about both our portfolio of marketed products and the advancement of our robust and dynamic pipeline," Solomon said on Monday.