Melatonin for jet lag: exactly when to take it

Medically reviewed by Muhammad A Jalil, Superintendent Pharmacist (GPhC Reg No: 2236161)

Published 2026-08-22 · Clinically reviewed 2026-08-22 · Updated 2026-08-23

When to take melatonin for jet lag — the timing that makes it work, doses UK clinicians prescribe, and how to combine it with light for faster adjustment.

Melatonin works for jet lag — but almost entirely because of when you take it, not just that you take it. The evidence-backed rule is simple: after flying east across five or more time zones, take melatonin at local bedtime (roughly 10pm to midnight) at your destination, starting the first night and continuing for up to four or five nights. Take it at the wrong time of day and it can pull your body clock the wrong way and make the fog worse. Here is how to get it right, in both directions.

Why jet lag happens

Your body runs on an internal clock — the circadian rhythm — that controls when you feel sleepy, hungry and alert. Flying across time zones outpaces it: the clock keeps releasing its own melatonin and winding alertness up and down on home time. The result is the familiar package of 3am wakefulness, daytime heaviness, poor concentration and an unsettled stomach. Left alone, the clock drifts into line by about one time zone per day — a week of feeling wrong after a London-to-Singapore flight. Timed melatonin, used well, can roughly halve that.

Eastward travel is harder than westward. Flying east asks you to sleep earlier than your body wants, and the clock resists advancing; flying west merely asks you to stay up later, which most people manage with coffee and willpower.

The timing rules that matter

Flying east (Europe to Asia, the UK to the Middle East, the US back to the UK):

Take melatonin at local bedtime at your destination — between about 10pm and midnight local time.
Start on your first night there (or, on an overnight flight landing in the morning, some clinicians advise a dose at the destination's bedtime while still in the air).
Continue nightly for up to four or five nights, stopping once your sleep has settled.

Flying west: melatonin matters less — staying up until local bedtime usually does the job. If you wake stubbornly early (4–5am), a dose in the second half of the night when you wake can help push the clock later, though the benefit is smaller than for eastward trips.

The mistake to avoid: taking melatonin in the morning or early afternoon at your destination. Melatonin signals "night is starting" — at the wrong clock time it shifts you in the wrong direction.

Dose and what to expect

Trials have used 0.5 mg to 5 mg; around 2–3 mg of standard (immediate-release) melatonin taken at destination bedtime is a common, sensible prescription, and going higher mainly increases next-day grogginess rather than benefit. Immediate-release suits jet lag better than prolonged-release forms, whose slow profile is designed for staying asleep, not for delivering a clear clock signal.

In the UK, melatonin is a prescription-only medicine — it is not available off the shelf as a supplement the way it is in the US, and quality-controlled dosing is one genuine advantage of the prescribed route. It is generally well tolerated for short courses: the common side effects are next-morning drowsiness, headache or vivid dreams, all settling when you stop. It is not recommended in pregnancy or while breastfeeding, and people with epilepsy or on blood thinners such as warfarin should flag that in any consultation, as should anyone on sedating medicines.

If you have a long eastward trip coming up and jet lag reliably eats the first days, you can check your eligibility for a short course online — a UK clinician confirms melatonin suits you and prescribes the right number of tablets for the journey.

Light: the other half of the fix

Melatonin nudges the clock; light drags it. Used together they adjust you fastest:

After flying east: seek bright morning light at your destination and avoid bright light in the evening. One caveat for very long eastward hops (eight or more zones): for the first couple of days, avoid light in the very early morning and get it mid-morning instead, or the clock can shift the wrong way.
After flying west: get evening light and keep sunglasses on during the early morning.
On board, set your watch to destination time and sleep or wake to match if you can.

Add the boring-but-true basics — hydration, limiting alcohol in flight, a short nap of under 30 minutes if desperate — and most people function well by day two or three even on long eastward routes.

Frequently asked questions

Does melatonin actually work, or is it placebo?

It works. A Cochrane review of randomised trials found timed melatonin clearly reduced jet lag on eastward flights across five or more time zones, with benefit on ratings of overall jet lag severity. The catch in every positive trial is the same: the dose was taken at destination bedtime, not whenever travellers felt like it.

Should I take it on the plane?

For most itineraries, the first dose at destination bedtime is enough. On overnight eastward flights that land in the morning, a dose timed to the destination's night while airborne can start the shift early — reasonable if you have taken melatonin before without grogginess. Never take it before driving after landing.

Can I use melatonin for ordinary insomnia too?

The jet-lag dosing here is a short, timed course for clock-shifting. Longer-term melatonin for insomnia is a different, age-restricted prescription conversation in the UK, and persistent sleep problems deserve a proper review rather than rolling holiday leftovers into nightly use.

How many nights should I take it for?

Up to four or five at the destination, stopping sooner if you are sleeping at local time. If you are only away two or three nights, some travellers skip adjustment entirely and keep meetings aligned to home time instead — no tablet needed.