On Jun. 6, 1991, ICOS completed its IPO at at $8.00 per share for a total of $36 million. Oct. 10, 1989 ICOS was founded by David Blech and Isaac Blech, Robert Nowinski, Christopher Henney, and George Rathmann.

The company was focused on discovering, developing and commercializing treatments for inflammation and other serious diseases. ICOS was established with $33 million in private financing, the largest industry start-up financing to date, with Microsoft co-founder Bill Gates as the largest shareholder.

On Nov. 21 2003, Cialis (tadalafil), a PDE5 inhibitor discovered through a Glaxo Wellcome (GlaxoSmithKline) ICOS partnership, was approved by the FDA for treating erectile dysfunction (ED) under the name trade name Cialis. In 2006, ICOS was acquired by Eli Lilly for $34 per share or $2.3 billion.