From http://sciencenow.sciencemag.org/science-shots/:
" Enjoy your flight. Sildenafil--better known under its brand name Viagra--could help fight jet lag after east-bound flights, and it might prevent health problems from shift work, scientists say. Viagra triggers the release of a compound, cyclic guanine monophosphate, that helps regulate the body’s circadian rhythm. When hamsters injected with the drug were woken up 6 hours earlier than normal, they adjusted 25% to 50% more quickly than did controls, a team from Argentina report in this week's Proceedings of the National Academy of Sciences. The doses needed in humans could be lower than those used for Viagra's most popular purpose, they add."
I do not know whether there is study of any difference between jet lag in east-bound and west-bound flights. In my case, the jet lag is worse in east-bound flights.
Another study reported at http://www.news.harvard.edu/gazette/2007/05.17/99-marstime.html. Excerpts:
"People at a research hospital in Boston have been living 24-hour, 39-minute days. They were part of an experiment to show that the 24-hour human sleep-wake cycle can be adapted to other biological rhythms like the longer days on Mars.
And it appears to be a relatively easy thing to do. All that seems to be needed is two 45-minute exposures to bright light in the evening.
.......
While checking the biological clocks of young, healthy subjects, Czeisler's team made what he calls, "an amazing observation." They knew that all people don't operate on the same clocklike 24-hour cycle, but the differences they found were startling. The 12 men and women in the Mars study, who were 22 to 33 years old, showed circadian periods ranging from 23 1/2 to 24 1/2 hours.
These natural differences cause some people to jump energetically out of bed in the morning, or to enjoy staying up late. Those with less than 24-hour brain rhythms tend to go to bed earlier and get up earlier. They are morning people. Those with a 24-hour-plus rhythm tend to stay up later. They are evening people. "Such individuals would have no trouble adjusting to a Martian day," Czeisler notes.
.....
In other words, Czeisler and his team squeezed extra minutes into the subjects' biological day simply by exposing them to bright light for 90 minutes each evening. The switch seems to work by resetting the time when humans begin to release a hormone called melatonin, which gets their bodies ready for sleep."
