Viagra improves blood flow

The World Anti-Doping Agency (Wada) has confirmed it is considering whether to include Viagra in its list of banned substances in international sports.

Wada believes sildenafil (Viagra) enhances athletic performance, particularly in high-pollution locations such as Beijing and London.

A spokesman told BBC Sport: "Wada is monitoring this substance.

"It is currently funding a research project on the performance-enhancing potential at various altitudes."

Sildenafil citrate drugs such as Viagra are intended to alleviate erectile dysfunction but Wada is conducting research into the drug to discover if it also enhances athletic performance with the results expected next year.

Wada updates its list of prohibited drugs annually and could add Viagra before the Games in London in 2012.

No action can currently be taken on athletes who have Viagra in their system because it is not illegal.

As well as boosting the blood supply to muscles - helpful in sprinting - the drug may also enhance endurance, especially when competitors are breathing in polluted conditions or at high altitudes.

Victor Conte, who ran the Bay Area Laboratory Cooperative (Balco) and supplied banned substances to top competitors such as sprinters Marion Jones and Dwain Chambers, has claimed of Viagra: "All my athletes took it. It's bigger than creatine [a legal muscle-building supplement]".