Traces of the drug in competitors' urine samples are becoming so widespread the World Anti-Doping Agency (Wada) is considering adding Viagra to the list of substances banned in international sports.
Christian Ayotte, head of a Wada-accredited laboratory in Montreal, Canada, said she regularly identifies Viagra, and other similar drugs, in urine samples from male athletes.
"Each time there is a seizure of banned drugs you can be sure that there's Viagra and Cialis found as well," she said.
At present no action is taken because the drug, which is widely available on the internet, is not illegal.
Experts believe Viagra could help in events requiring explosive power, such as sprinting. The drug works by dilating blood vessels allowing more blood to reach the penis. This action could also allow more oxygen and nutrients to reach muscles.
Other experts suggest the drug, which allows couples to have longer sex sessions, could also help with endurance sports, like marathons and cycling.
Don Catlin, an American expert on doping, said he had suggested several years ago that Viagra could be used to enhance athletic performance.
"I thought there was some reason to be concerned about it and to put it on [Wada's banned] list," he told the Sunday Times newspaper.
A study of cyclists who took sildenafil citrate (the scientific name for Viagra) while racing at altitude found it reduced their time over 6km by 15 per cent.
