Mama Always Said You'd Go Blind

This just in from erectile dysfunction (ED) central: Taking Viagra and Cialis might make you blind.

Old wives' tales about going blind from, well, certain activities aside, the Food and Drug Administration says 38 people who took Viagra and four who took Cialis went blind. Viagra, the most popular drug for treating ED, is made by Pfizer (NYSE:PFE). Cialis is sold by Eli Lilly (NYSE:LLY) and Icos (NASDAQ:ICOS). As yet, there's no confirmation that the drugs are to blame.

Although Viagra was the first such impotence treatment on the market, it now faces increasing competition from Cialis and Levitra, which is sold by Bayer AG (NYSE:BAY) and GlaxoSmithKline (NYSE:GSK). There's been a noticeable decline in Viagra's revenues: sales were $1.68 billion in 2004, an 11% drop from the previous year. But as attention-grabbing as such news is, it's important to keep in mind that while Viagra is one of Pfizer's best-known drugs, its sales amount to less than 5% of Pfizer's total revenue.

The fallout from this news is that Pfizer may be forced to include a warning about blindness on Viagra's label. Mom's warnings about going blind could kick in -- and could cause an additional decline in sales. That's conceivable, I suppose.

However, I don't expect the concerns about side effects to dampen Pfizer's long-term prospects. (And Philip Durell, analyst of our Motley Fool Inside Value newsletter, would agree -- Philip recommended Pfizer to his subscribers back in March.) Indeed, fears of side effects have dominated drug-industry headlines for months: Merck (NYSE:MRK) pulled pain treatment Vioxx from the market last year after reports that the drug caused heart problems. Pfizer was told to pull a similar treatment, Bextra, and sales of its other pain drug, Celebrex, have slipped.

When bad buzz surrounds a solid company like Pfizer, I'm reminded that you can profit from panic. If investors overreact to bad news, then it's time to dig out the trusty value investing calculator and crunch some numbers.

Rest assured that we're following this Viagra news at Inside Value HQ. We're keeping a cool head. If you'd like to read the fruits of our value investing labor, or see some other companies we think are great bargains, click here for a free 30-day trial.

Nick Baker doesn't take Viagra, Levitra, or Cialis -- not that there's anything wrong with that. He has no financial interest in any of the companies mentioned in this story. Merck is a Motley Fool Income Investor recommendation. View Nick's profile here. The Motley Fool has a disclosure policy.