Viagra: The little blue pills have been dubbed 'Vitamin V' by athletes

Viagra's use as a performance enhancer in the bedroom is well known.

But now athletes are now finding the little blue pill improves their abilities on the sports field.

The World Anti-Doping Agency, the body that monitors the use of drugs that enhance sporting prowess, is considering adding Viagra to its list of illegal substances.

The pill is currently not an illegal substance in world sport.

But athletes have found that the drug, normally prescribed as a cure impotence, boosts blood flow to their lungs.

WADA is to conduct research into the effects of the drug, but the results are expected until next year.

So competitors at the Beijing Olympics this year will still be able to take Viagra, which has come to be nicknamed 'Vitamin V' in sporting circles.

Christiane Ayotte, a scientist at a laboratory accredited by WADA said she regularly finds Viagra and a similar drug, Cialis, in the urine samples of male competitors.

'Each time there is a seizure of banned drugs you can be sure that there's Viagra and Cialis found as well,' she said.

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

Research on cyclists who took sildenafil citrate - the chemical name for Viagra - found that it improved their time over 6km by 15 per cent.

The 2006 research, in the Journal of Applied Physiology, found that it did not work for all athletes and was not a significant performance enhancer at sea level.

Last month at the Giro d'Italia, Italy's biggest bike race, one competitor, Andrea Moletta was suspended after his father's car was searched and syringes hidden in toothpaste tubes were found - along with 82 Viagra pills.

Victor Conte, who ran the Bay Area Laboratory Co-Operative, which supplied banned drugs to leading U.S. athletes, including runners Marion Jones and Dwain Chambers said of Viagra: 'All my athletes took it. It's bigger than creatine .

A further reason why it is turning up is because it may counteract the effects of steroids, used by athletes to build their muscles, which can induce impotence.

A WADA spokesman said it was 'monitoring this substance and is funding research on performance enhancing potential.'

A spokesman for Pfizer said: 'We are aware it's an issue, but we don't promote Viagra in cases where it's not a recommended use.

'Its pharmaceutical use is for erectile dysfunction, and we don't encourage its use other than what it's approved for.'