Viagra used in combination with light could help jetlag symptoms

A team of Argentine scientists found the drug helped hamsters recover up to 50% faster from forward shifts in their daily time cycles.

However, the drug only worked in conjunction with light therapy, and only in one time direction - the equivalent to flying eastbound.

The study features in Proceedings of the National Academy of Sciences.

In mammals, the light-dark cycle regulates the body's biological clock, which promotes activity during the daytime, when it is light, and sleep at night.

Time shift

The researchers from the National University of Quilmes shifted the light-dark cycle of hamsters six hours forwards, by switching on lights six hours earlier than usual.

They then monitored the hamsters' running wheel activity to assess when their body clocks had adjusted to the new time cycle - the hamsters are active in the day but stop running when the lights go out.

Injection of Viagra before the time shift meant the hamsters adjusted to the new time cycle faster, even when low doses of the drug, which did not cause penile erections, were used.

Viagra, the drug sildenafil, was originally developed for the treatment of high blood pressure and angina, and is used to treat erectile dysfunction.

Viagra used in combination with light could help jetlag symptoms

When used without the shifts in light, the drug did not induce changes in the hamsters' activity, so it seems to work by enhancing the light-induced response.

Dr Diego Golumbek, who led the research, said the drug seemed to work via a molecule called cGMP which is known to have a role in setting the body's time clock - it is present at higher levels during the day.

The Viagra blocks the activity of an enzyme which breaks down cGMP, allowing higher levels to build up.

One direction only

Dr Golumbek said the fact that different mechanisms may be used to slow down and speed up the body clock explains why Viagra only worked when the lights were switched on early, not late.

Professor Robert Lucas, from Manchester University, said although looking for ways adjust biological clocks was important, regulating light exposure was the most widely accepted strategy for doing this.

He said the new research raised the possibility of using Viagra in conjunction with this light treatment, but he added: "We will have to wait for more research to know whether this will work in humans."

Pfizer, the makers of Viagra, said the drug should only be used in accordance with the approved labelling.