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Viagra pills in an undated file photo. The male impotence drug Viagra may be useful for treating jet lag as well, according to Argentine researchers who gave it to hamsters made to feel like rodent globe-trotters. [Reuters]

WASHINGTON - The male impotence drug Viagra may be useful for treating jet lag as well, according to Argentine researchers who gave it to hamsters made to feel like rodent globe-trotters.

The researchers manipulated the schedule of turning lights on and off to induce jet lag in the laboratory animals, they reported Monday in the Proceedings of the National Academy of Sciences.

Adult male hamsters given Viagra, also called sildenafil, recovered from jet lag up to 50 percent faster than hamsters that were not given it, the researchers said.

The scientists stopped giving the hamsters the highest dose they had been using in the experiment due to a certain side effect.

"However, we used the intermediate dose for the rest of the experiments because at that dose animals did not manifest the effects of sildenafil-induced penile erections," they wrote.

Flying across multiple time zones can confuse one's sleep-wake cycle, resulting in the condition called jet lag, marked by insomnia, sleepiness and difficulty concentrating.

Researchers Patricia Agostino, Santiago Plano and Diego Golombek of the Universidad Nacional de Quilmes in Buenos Aires gave doses of Viagra to the hamsters at night, then switched on bright lights six hours early to simulate eastbound flight.

They judged how well the hamsters adjusted to the changes by observing when they began running on exercise wheels.

The drug helped the rodents cope with jet lag only when given before the equivalent of an eastbound flight, not the reverse when they delayed turning on lights to simulate westbound travel, the study found.

The researchers said the findings suggested that Viagra could be useful to help people cope with jet lag or shift work. They said the dose needed for such uses could be lower than the one used for treatment of erectile dysfunction.

Viagra interferes with an enzyme that lowers levels of a naturally occurring compound that plays a role in the regulation of the circadian cycle, the body's internal clock, the researchers said.

Viagra is marketed by Pfizer, the world's largest drug maker. The U.S. Food and Drug Administration approved it to treat erectile dysfunction in 1998.