This just in, from BBC News. BBC reports that 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 was recently published in Proceedings of the National Academy of Sciences.
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 were used.
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.
