Jet-lagged? Pop a Viagra!

A shot of the male impotence drug may help flight crews recover their normal sleep cycles, says a study.

A shot of Viagra may one day help shift workers and flight crews recover their normal sleep cycles, according to a study on hamsters released Monday.

Viagra, otherwise known as sildenafil, could be "useful in other circadian disorders that involve poor synchronisation with the environment, including delayed sleep-phase syndrome and adaptation to changing light schedules," said the study published in the Proceedings of the National Academy of Sciences.

Researchers at Argentina's National University at Quilmes in Buenos Aires injected male hamsters with small amounts of the drug and switched off the lights six hours earlier, which researchers compared with taking an east-bound flight, as would occur from the Americas to Europe.

Hamsters receiving a dose of the drug adapted 20-50 per cent more quickly to the new schedule than hamsters receiving a placebo, the study said, as judged by how quickly they resumed running on their exercise wheels.

However, the trick worked only when moving the schedule ahead, as on the so-called eastbound change, without helping hamsters shifted six hours in the other direction.

Mammals, such as humans and hamsters, regulate their circadian rhythms by releasing chemicals in the brain, such as melatonin.

The National Academy of Sciences was established by the US Congress in 1863 to advise the United States on science, medicine and engineering matters.