Japanese researchers have discovered why travelers get jet lag: it's all in the hormone vasopressin. And their discovery could help lead the way toward creating a pill to curb those restless nights and afternoon slumps.

Jet lag, as every long-distance traveler knows, disrupts the body's normal circadian rhythms, or body clocks, and causes some very unpleasant effects such as disturbed sleep, dizziness, and fatigue.

The severity of the symptoms usually depends on the number of time zones you've crossed, the length of your stay, and the direction of travel. Symptoms tend to be worse the more time zones you cross and the shorter the trip is, but on average, it takes most people about one day to adjust for every hour difference.

In mice studies, study coauthor Hitoshi Okamura of Kyoto University and his team found that the brain region that "drives the master internal clock, the suprachiasmatic nucleus (SCN), was full of receptors for vasopressin," LiveScience reported. Previous research has linked vasopressin to feelings of love and generosity, they added.

To test how the vasopressin receptors functioned in the brain's clock region, the team genetically engineered mice that lacked the brain receptors for the hormone. Then they subjected the mice to a fully disrupted day and night schedule, to simulate international travel. The genetically altered mice immediately adapted to the new cycle.

The scientists then recreated the experiment in normal mice but suppressed the vasopressin's action in the brain via an experimental compound. While those mice didn't adjust as quickly as the mice that lacked vasopressin receptors, they did become in sync with the new schedule in three days.

LiveScience added that while the mice didn't exhibit any negative side effects from the compound, obviously more studies will be needed before humans can start popping jet lag pills. So for the time being, you can curb some of the ill effects from international travel by staying hydrated throughout the flight by drinking plenty of water and avoiding caffeine and alcohol, which can disrupt sleeping schedules and further dehydrate your body.

The findings were published online Oct. 4 in the journal Science.