When to Take Melatonin for Jet Lag: A Timing Guide

Why timing matters more than dose

The instinct is to take melatonin when you feel sleepy. That instinct is wrong. Melatonin is not a sedative — it is a phase-shifting signal. The goal is to move your body clock earlier or later, not to force sleep.

Your body begins producing melatonin about two hours before your natural sleep onset. This moment is called DLMO — dim-light melatonin onset. Taking a supplement at bedtime means you are adding to melatonin your body is already making. The signal is redundant. Nothing shifts.

Taken at the right time — several hours before your own DLMO rises — exogenous melatonin tells your circadian clock that darkness has arrived earlier than expected. This is the mechanism that shifts your clock forward. The Cochrane Review by Herxheimer and Petrie (2002), covering 10 randomised trials, found melatonin taken close to target bedtime significantly reduced jet lag symptoms. The key phrase is target bedtime — the time you want to sleep at the destination, not the time you currently feel like sleeping.

Flying east vs. flying west: two different protocols

The direction you travel determines which way your clock needs to shift, which determines when melatonin will actually help.

• Eastward travel (e.g. Vancouver to London, +8 hours): You need to advance your clock — go to bed and wake up earlier than your body currently wants to. Take 0.5mg melatonin at 6–8pm destination local time, starting the evening you arrive. This places the supplement several hours before your shifted DLMO, which is the window where it produces a phase advance. Combine with bright light in the morning at the destination (7–9am) and avoid light after 3pm local time on your first 2–3 days.
• Westward travel (e.g. Vancouver to Tokyo flying west, -9 hours): You need to delay your clock — push your sleep time later. Take 0.5mg melatonin at your target destination bedtime (10–11pm local). Morning light at the destination is helpful; avoid bright light in the early evening. Westward shifts are generally easier because the human circadian clock naturally runs slightly longer than 24 hours — your body is already biased toward staying up later.

What dose to take

Pharmacies sell melatonin in 3mg, 5mg, and 10mg doses. These are far higher than the physiological amount your body produces. Research consistently shows that 0.5mg is as effective as 5mg for phase shifting — and causes significantly less next-day grogginess.

High doses can also desensitise melatonin receptors over repeated use, reducing effectiveness. If you can only find 3mg tablets, cut them in half. Liquid melatonin in 0.5mg doses is available at most health food stores.

Avoid taking melatonin with alcohol. Alcohol suppresses natural melatonin production and will counteract the shift you are trying to create.

What not to do

Do not take melatonin at your home bedtime when you arrive at the destination. For eastward travel, your home bedtime is likely early morning at the destination — taking melatonin then could lock your clock to the wrong time.

Do not take melatonin every night indefinitely. It is a short-term phase-shifting tool. Three to five nights is sufficient for most trips. Long-term nightly use at high doses can suppress your body's own melatonin production.

Do not rely on melatonin alone. Light exposure is the strongest circadian zeitgeber (time-giver). Melatonin accelerates a shift that light and darkness are already creating. Used without attention to light, melatonin has a much weaker effect.