Sildenafil, which was originally developed by the company Pfizer for the treatment of high blood pressure and angina, works by interfering with an enzyme that reduces levels of a naturally occurring compound, cyclic guanine monophosphate (cGMP), which plays a role in many processes, such as erections.

In the brain, cGMP also works in a region that regulates the circadian cycle, the body's daily clock that governs the waxing and waning of hormones and the urge to sleep and to wake.

Today, in the Proceedings of the National Academy of Sciences, a paper describes experiments on hamsters to show whether Viagra can affect the body clock.

Patricia Agostino, Santiago Plano and Dr Diego Golombek of the Universidad Nacional de Quilmes in Buenos Aires, injected hamsters with sildenafil at night before turning on bright lights six hours early, as would occur if flying from America to London.

The team observed how easily the hamsters adjusted by noting how soon the nocturnal animals began running on their exercise wheels when the lights went out.

They found that sildenafil boosted the ability of hamsters to recover 25 to 50 per cent quicker than untreated animals. Sunlight is thought to be a key influence on the body clock by its involvement in a neurochemical pathway in which cGMP is involved, and in this way the drug is thought to make the brain more sensitive to the effects of light, Dr Golombek said.

However, the drug only worked when applied before an advance in the light/dark cycle, equivalent to an eastbound flight.

Encouragingly, Viagra worked at doses low enough not to trigger erections, though Dr Golombek stressed that human tests would be needed to confirm that this was also true for people.

The scientists believe that frequent fliers and shift workers may well benefit from moderate doses of sildenafil, with passengers probably taking it during flights.

"Shift work and chronic jet lag reduce mental acuity and increase the risk of a number of medical problems," Dr Golombek said.

"A potential jet-lag treatment for advancing cycles could also be important for the safety of counter-clockwise rotating shift work and the potential long-term health consequences for airline crews regularly crossing time zones."

Other drugs that raise levels of cGMP may have a similar effect, Dr Golombek said. "The use of sildenafil is particularly appealing because this drug has been thoroughly studied in terms of its pharmacological effectiveness and safety.

"Taking into account that jet lag, as well as other circadian disorders, is increasingly common and has profound effects on quality of life, I believe this research is particularly relevant since it opens a completely original way of dealing with this kind of disarrangement."

A Pfizer spokesman said Viagra was available only by prescription for the treatment of erectile dysfunction and should always be used in accordance with the approved labelling.