Jet lag, which appears after a long lasting transmeridian flight, is generally considered as a consequence of a desynchronization of circadian rhythms. After a recall of the circadian physiology, a modern view of the physiopathology is proposed. The major idea that emerges from these data is that only the wake-sleep rhythm may adapt itself quickly during jet lag and therefore it constitutes a good therapeutic target for physicians. We focus on the modalities of a light pharmacological aid to counteract jet lag. This punctual aid should help passengers to restore an adapted wake-sleep rhythm as quickly as possible. From this point of view, hypnotics may constitute a good indication. Finally, we suggest that the use of psychostimulants could also be interesting in very exceptional circumstances.