Melatonin isn't a sleeping pill — it's a timing signal. Taken at the wrong time, it pushes your clock the wrong way.

Melatonin has proper trials behind it for jet lag. It’s also easy to use backwards. A dose taken at the wrong hour doesn’t just do nothing. It can nudge your body clock in the opposite direction from the one you’re flying.

This guide covers what the evidence says about dose and timing, and how that changes depending on which way you’re flying. None of it is medical advice. Talk to your doctor before you take melatonin, and especially before you combine it with other medication.

Does melatonin actually work for jet lag?

On long flights, the trials say yes. A 2002 Cochrane review of the randomised trials, still the benchmark, found that nine of ten trials showed melatonin, taken close to the target bedtime at the destination (10pm to midnight), reduced jet lag after flights crossing five or more time zones S5. The reviewers’ conclusion was blunt: melatonin is “remarkably effective in preventing or reducing jet-lag” S5.

Two details from that review matter for planning a trip:

• The benefit is likely to be greater the more time zones you cross S5.
• It is likely to be smaller for westward flights S5.

The same review recommends it for adults flying across five or more time zones, particularly eastward, and especially if jet lag has hit them hard before. For two to four time zones, it says travelers can use it if they need it S5.

What does melatonin do to your body clock?

For jet lag, think of it as a timing signal. It does make you sleepy too, but only at certain times, and mixing the two jobs up is where most of the confusion starts.

Melatonin is both a chronobiotic and a hypnotic S1. The chronobiotic part shifts the timing of your body clock. The hypnotic part makes it easier to fall asleep and stay asleep S1.

The sleepy effect depends on when you take it. Taken during your body’s night, when your own melatonin is already high, neither a small 0.3 mg dose nor a large 5 mg dose made people sleepier. Taken during your body’s daytime, both did S1.

The clock-shifting effect also depends on timing, and this is the part that decides whether a dose helps or hurts:

• Taken in the late afternoon or early evening, a few hours before your body starts making its own melatonin, it shifts your clock earlier S1. That’s a phase advance, the change you need flying east.
• Taken in the morning, a few hours after your usual wake-up time, it shifts your clock later S1. That’s a phase delay, the change you need flying west.

Put those two lists side by side and the risk is obvious. A pill swallowed at a convenient hour, rather than the right one, can push you the wrong way. The Cochrane reviewers saw the same thing in the trials: taken at the wrong time, early in the day, melatonin “is liable to cause sleepiness and delay adaptation to local time” S5.

When should I take melatonin flying east?

Close to bedtime at your destination. That’s what the trials used: in nine of the ten, melatonin was taken near the target bedtime at the destination, 10pm to midnight local time, and it reduced jet lag S5. It’s the practical default, and it’s the one with human field evidence behind it.

Lab work adds one twist. Studies that map how the clock responds to melatonin find the biggest shifts from doses taken earlier, in the afternoon of your body’s day S1. The cost is that melatonin taken during your body’s daytime makes you sleepy S1. A drowsy afternoon on the first day of a trip is a bad trade for most people. That’s why the practical advice stays at bedtime.

Flying east, the benefit in the trials was larger than going west, and larger the more time zones you cross S5.

When should I take melatonin flying west?

The evidence is weaker here. The Cochrane review found the benefit is likely to be smaller on westward flights S5. Your body clock also has a head start going this way. Its natural cycle runs at about 24.2 hours, so it drifts later more easily than earlier S1. For more on why direction matters so much, see east vs west: why one direction wrecks you.

If you use it, the same default applies: close to bedtime at your destination S5. The lab work says a morning dose is what pushes the clock later S1, but a morning dose lands in your body’s daytime, and melatonin taken then makes people drowsy S1. Don’t try that on a day you have to drive or work.

Melatonin timing by direction

	Flying east	Flying west
What your clock needs	Earlier (advance)	Later (delay)
Practical default	Close to local bedtime, 10pm to midnight S5	Close to local bedtime, 10pm to midnight S5
What lab work adds	Bigger shifts from afternoon doses, at the cost of daytime sleepiness S1	Morning doses delay the clock, and can leave you drowsy S1
Trial evidence	Stronger; recommended for 5+ time zones S5	Benefit likely smaller S5
Watch out for	A dose early in the day: sleepiness and slower adjustment S5	Same S5

How much melatonin should I take?

Less than you might think. In the trials, daily doses between 0.5 and 5 mg were similarly effective at reducing jet lag S5. People fell asleep faster and slept better on 5 mg than on 0.5 mg, and doses above 5 mg appeared to be no more effective S5.

The 2019 review adds a distinction between shifting and sleeping. It describes doses of 0.5 mg or less as physiological, meaning close to what your body makes, and 1 to 5 mg as pharmacological S1. Both 0.5 mg and 3 mg produced shifts of a similar size, but 3 mg shifted the clock more reliably S1.

Question	What the evidence says
Does 0.5 mg work?	Yes. Similar effect on jet lag to higher doses in the trials S5
Is 5 mg better?	Faster sleep onset and better sleep than 0.5 mg; jet lag effect similar S5
Anything above 5 mg?	Appears to be no more effective S5
3 mg vs 0.5 mg for shifting the clock	Similar size of shift; 3 mg more reliable S1
Slow-release	2 mg slow-release was relatively ineffective S5

That last row surprises people. The Cochrane reviewers suggested that a short-lived higher peak of melatonin works better than a slow trickle S5. For jet lag, plain fast-release tablets are what the trials support.

Is melatonin safe to take for jet lag?

The Cochrane review found occasional short-term use appears to be safe, and other side effects were uncommon S5. Two groups stood out. Case reports suggest that people with epilepsy, and people taking warfarin, may come to harm from melatonin S5. If either applies to you, don’t take it without talking to your doctor first.

The review also flagged product quality. Its authors called for routine pharmaceutical quality control of melatonin products S5. The 2019 review makes a related point for athletes: check that melatonin isn’t prohibited under your sport’s drug code, and buy it from a reputable supplier so the dose on the label is the dose in the tablet S1.

If you’re pregnant, breastfeeding, or on any regular medication, ask your doctor before you take it. This guide doesn’t cover melatonin for children; our guide to jet lag with kids explains why.

Can I buy melatonin at my destination?

Don’t count on it. If you rely on melatonin, check the rules for where you’re going before you leave, and pack what you need.

Does melatonin work better with light?

Yes. Light and melatonin can each shift your clock on their own, and their effects add up, particularly for phase advances S1. Used together they should do more than either one alone S1. That makes eastward trips, where you need an advance and the evidence for melatonin is strongest, the place where combining them pays off most.

The catch is that light has timing rules of its own, and they run on the same body clock. If you’d rather not work out both schedules by hand, the jet lag calculator builds the plan for your flight. It includes melatonin only if you want it, and times it off your body clock rather than the airline’s.

If you’ve heard that melatonin on the plane or a glass of wine does the same job, those claims get their own check in jet lag hacks, tested against the science.