Jet lag is caused by the body’s inability to adjust its circadian rhythm to a new time zone. Much of our understanding of jet lag has come from research on the degu, a small rodent that neither flies nor experiences jet lag. This remarkable rodent can reset its circadian rhythm very easily. Orally administered doses of the sleep hormone melatonin have aided the degu in readjusting its sleep schedule, which makes this a possible treatment for humans as well.