Jet Lag and Melatonin Dosing: How Much and When to Take It

In our article on melatonin and jet lag, based on the Cochrane review, we cover the evidence for whether melatonin works at all. Here we assume that question is already answered, and focus purely on practice: which dose to pick, exactly when to take it, and whether the protocol differs between eastward and westward flights.

Melatonin taken exogenously in the context of jet lag works differently from a typical sleep medication — its main job isn't to induce drowsiness per se, but to deliver the brain a timing signal similar to the one the pineal gland normally generates in the evening. The suprachiasmatic nucleus (SCN), the central biological clock in the hypothalamus, reads blood melatonin levels as one of its main cues about the current phase of the day. Giving melatonin within a specific window relative to the traveler's internal clock can shift that clock toward the new time zone faster than it would adjust on its own, at its natural pace of about one hour per day.

This explains why timing matters more than dose: melatonin taken at the wrong moment relative to the internal clock sends the brain a misleading phase signal — it might, for instance, suggest it's already "biological evening" when the body is actually still in the daytime phase of the old time zone, which increases sleepiness at the wrong moment and, in extreme cases, slows adaptation instead of speeding it up.

The dosing protocol genuinely differs depending on flight direction, which stems from a fundamental asymmetry in how easily the human biological clock shifts its phase. Eastward flight requires a phase advance (you need to fall asleep and wake up earlier than the old clock would dictate) — which is physiologically harder, because the human free-running circadian rhythm is slightly longer than 24 hours and naturally "wants" to lengthen, not shorten. Westward flight requires a phase delay, which aligns with that natural tendency and is therefore usually easier to tolerate even without any intervention.

The Cochrane review states directly that the benefit of melatonin is clearer with a greater number of time zones crossed and particularly on eastward flights — that's the direction that gives the body the most trouble, so an external phase signal like melatonin has the most to offer there. On westward flights, especially those covering fewer than five time zones, many travelers adapt well without any intervention, and melatonin becomes optional.

Many over-the-counter melatonin supplements on the market, especially in North America, contain 5, 10, or sometimes even 20 mg per capsule — far more than the doses used in most clinical trials on jet lag. The Cochrane review data show that this "more is better" approach has no support in the jet lag context: a plateau effect occurs already at 5 mg, and doses above that level bring no additional benefit in symptom reduction, though they could theoretically increase the risk of next-day grogginess (a so-called "melatonin hangover") if taken too late relative to the planned wake-up time.

An interesting, often underappreciated detail from the same review is that the slow-release form performed relatively worse than the standard form — a short, clear peak in blood melatonin concentration appears to be a more effective phase signal for the SCN than a stretched-out, lower release of the same total dose. This runs against the intuition that a "longer-acting" product should be better for sustaining the effect through the night.

This myth is especially persistent because we intuitively associate supplements with a "more equals stronger effect" pattern, which is true for many substances with dose-proportional pharmacological action, but not for melatonin in its role as a phase signal — here what matters most is when the signal reaches the biological clock, not how strong it is above a certain minimum level.

Melatonin for jet lag is one of the few supplements with such a precise, systematic-review-based dosing protocol — and at the same time one of the more frequently misused, because popular advice focuses on "whether to take it" rather than "when to take it." Understanding that timing relative to the target bedtime and flight direction determine the outcome more than dose size turns melatonin from a random supplement into a tool you can deliberately tailor to a specific trip.