Lilly ICOS, which manufactures Cialis, said there had been a small number of cases of NAION in people taking the drug.

BBC: NEWS | Health | Sight warning on impotency drugs

Lilly and ICOS have already filed their impotence drug, Cialis, with the U.S. Food and Drug Administration.

FORBES: Impotence Drug Won't Cure Bayer's Ailment

Through sponsorships and spokesmen, the Lilly-Icos team hopes to link its drug to longer duration, speed of action and athletic prowess.

FORBES: Let's Talk About Sex