Athletes may be using Viagra for competitive edge

But experts are divided over whether it actually offers athletes an edge.

Some sports authorities say the drug is now finding a following among athletes. It isn't clear how many might be taking it in hopes of improving athletic performance.

It also has attracted the attention of the World Anti-Doping Agency. The agency is studying Viagra's effects in athletes, but hasn't yet banned it. Viagra is not on the International Olympic Committee's list of prohibited drugs, so athletes can take it at the Beijing Olympics.

Viagra, also known as sildenafil, is manufactured by Pfizer Inc. It originally was developed as a heart drug; its use as a treatment for erectile dysfunction was accidentally discovered.

The drug works by increasing the effects of nitric oxide, which makes blood vessels expand. That should theoretically allow blood cells to get more oxygen from the lungs. It also might improve heart function.

Viagra also is approved to treat pulmonary hypertension, a condition in which the lungs' blood vessels tighten. Doctors have used the drug experimentally to treat pregnant women with high blood pressure and to ward off jet lag.

But whether Viagra makes athletes faster, higher or stronger is uncertain.

"Just because you have more nitric oxide doesn't mean that you are going to be a better athlete," said Anthony Butch, director of the Olympic Analytical laboratory at UCLA. "If you have all the nitric oxide you need, and if you generate more from Viagra, it's not clear what effect that would have."

Still, some preliminary studies have shown that cyclists taking Viagra improved their performances by up to 40 percent.