Although there's not enough data to confirm a direct effect of erectile dysfunction drugs on hearing loss, the FDA nonetheless issued a warning on Thursday about Pfizer's (NYSE:PFE) Viagra, Eli Lilly's (NYSE:LLY) Cialis, and Levitra, which is marketed by GlaxoSmithKline (NYSE:GSK), Schering-Plough (NYSE:SGP), and Bayer.

The agency said it had received 29 reports of hearing loss in patients taking the erectile dysfunction drugs. These reports go back as far as 1998, when Viagra was approved, so we're only talking about a few cases a year. All the manufacturers will have to add the warning to their labels.

The drugs may make you blind and deaf, but my male intuition says the new warning labels are unlikely to have much effect on sales. But Fools know that numbers are often more reliable than intuition, so I combed through the 10-Ks to bring you proof that men and their partners could care less about side effects -- as long as the drugs work.

2004

2005

2006

Viagra

$1,678

$1,645

$1,657

Cialis

$552

$747

$971

Levitra

$90

$73

$80

Total

$2,320

$2,465

$2,708

Worldwide sales; all figures in millions.

As you can see, the May 2005 FDA warning about the drugs causing blindness in 42 patients doesn't seem to have caused a decline in sales.

This is certainly no Merck (NYSE:MRK) Vioxx issue. It's a lot closer to Amylin Pharmaceuticals' (NASDAQ:AMLN) issue last week with its diabetes drug Byetta; a few incidents make the FDA jumpy enough to issue the warning. Any investor jumpiness should be looked at as a buying opportunity for Foolish investors.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.