Does melatonin actually help with jet lag?
Yes, but with caveats. Melatonin is one of the most studied interventions for jet lag, and the evidence is reasonably strong that it helps when used correctly. A Cochrane review of 10 trials found that melatonin reduced jet lag in travellers crossing five or more time zones when taken close to bedtime at the destination.
The important phrase is "when used correctly." Most people get the dosage wrong, the timing wrong, or both, and then conclude it doesn't work.
The dosage mistake almost everyone makes
The most common melatonin supplements sold in shops and pharmacies come in 3mg, 5mg, or even 10mg tablets. These are far higher than what the research supports for jet lag.
The evidence suggests that 0.5mg to 1mg is the optimal dose for jet lag purposes. At this level, melatonin acts as a circadian signal: it tells your brain "it's nighttime now" and helps shift your clock. At higher doses (3mg and above), it acts more as a sedative. You might fall asleep, but you're not necessarily shifting your clock, and you're more likely to feel groggy the next morning.
A study in the Journal of Pineal Research found that 0.5mg of melatonin was just as effective as 5mg at shifting circadian rhythms, with fewer side effects. More is not better here.
If you can only find 3mg tablets, cut them in half or quarters. It's not precise, but it's closer to the effective range than taking the whole thing.
When to take it
Timing matters more than dose, and the correct timing depends on which direction you're travelling.
Flying east (UK to Thailand, US to Europe, and so on): take melatonin at your destination bedtime on the evening of arrival and for 3 to 5 nights after. So if you want to sleep at 10pm Tokyo time, take 0.5 to 1mg at 9:30pm Tokyo time.
Flying west (UK to USA, Australia to UK, and so on): melatonin is less necessary for westbound travel because you're delaying your clock, which is more natural. If you want to use it, take it at your destination bedtime. It can help you fall asleep at the local time rather than staying up because your body is still on the old timezone.
Don't take it during the day or in the afternoon. Melatonin taken at the wrong time can shift your clock in the wrong direction and make jet lag worse. This is counterintuitive: how can a sleep supplement make things worse? But melatonin isn't just a sleeping pill. It's a timing signal. Taking it at 3pm tells your brain that 3pm is nighttime, which is the opposite of what you need.
How long to take it
For most trips, 3 to 5 nights is enough. Your circadian clock shifts by roughly one to two hours per day with good light exposure and melatonin support. Once you're sleeping at your target time without the supplement, stop.
There's no evidence that short-term use (a week or less) causes dependency or reduces your body's natural melatonin production. You can use it trip after trip without building tolerance.
What melatonin doesn't do
Melatonin is not a sleeping pill. It won't knock you out. If you take it at midnight when your body thinks it's 5pm, you won't fall asleep immediately. You'll be lying in the dark with a slight biological nudge towards drowsiness. It works best alongside other strategies: darkness, avoiding screens, and correct light exposure during the day.
It also doesn't fix travel fatigue. If you've just spent 12 hours in economy class, you'll feel rough regardless of your circadian alignment. Melatonin resets your clock. It doesn't repay sleep debt.
Side effects
At low doses (0.5 to 1mg), side effects are minimal. Some people report vivid dreams, which usually fade after a night or two. At higher doses, next-morning grogginess is common, which is the main reason to keep the dose low.
Melatonin is generally considered safe for short-term use in healthy adults. It can interact with some medications (blood thinners, immunosuppressants, diabetes medication). If you're on regular medication, check with your GP before using it.
In the UK, melatonin is a prescription-only medication, but low-dose supplements (often marketed as "food supplements") are widely available online. In the US, Australia, and most of Europe, it's available over the counter.
How to use it
Take 0.5 to 1mg, 30 minutes before your target bedtime in the new timezone, for 3 to 5 nights. Keep the dose low. Get the timing right. Combine it with morning light exposure for the fastest adjustment.