Jet lag isn’t tiredness from the flight — it’s your internal clock running on the old time zone while local life runs on the new one. That’s why it can’t be slept off in one night, and why the fix is about clock-shifting, not just rest.
The basic maths
The body clock naturally shifts by roughly an hour a day, so a 7-hour difference takes most people the best part of a week to fully absorb. Direction matters enormously: eastward travel is harder (you must sleep earlier than your clock wants — fighting biology) while westward is gentler (staying up later is something the clock does willingly). Short trips of 2–3 days across many zones are sometimes best handled by not fully adapting at all — keeping key events aligned to home-time alertness.
Light: the real medicine
Light is the clock’s master signal, and when you get it decides which way you shift:
- Flying east (e.g. UK → Asia): seek morning light at your destination and avoid bright light late in the evening — morning light pulls the clock earlier;
- Flying west (e.g. UK → USA): seek late-afternoon and evening light and go easy on very early morning light for the first days — evening light pushes the clock later;
- Get light timing wrong across big eastward hops and you can push the clock the wrong way — if you’ve ever felt jet lag get worse on day three, this is usually why. Sunglasses are a legitimate clock-management tool.
Sleep tactics that support the shift
- Start shifting bedtime 30–60 minutes per day toward destination time for 2–3 days before a big eastward trip;
- Set watches to destination time at take-off and behave accordingly on the plane — sleep or stay awake to match;
- On arrival, use short 20-minute naps to survive the day without draining night-time sleep pressure (see our napping guide);
- Time caffeine for destination-morning only — and remember its half-life when tempted at 4pm local (see caffeine and sleep);
- Go easy on alcohol in-flight: dehydration plus fragmented sleep is a poor start to a clock shift.
Where melatonin fits — the UK position
Taken at the right time (close to destination bedtime, mainly for eastward travel across 5+ zones), melatonin has reasonable evidence for reducing jet lag. In the UK it remains prescription-only, so it’s a pre-trip GP conversation rather than an airport purchase — the how and why are covered in melatonin in the UK. Supermarket melatonin gummies abroad carry the dose-accuracy problems described in that article. As for sleeping tablets: a zopiclone-style sedative doesn’t shift your clock — it just sedates you on the wrong time zone, and mid-flight use adds immobility and next-day grogginess. Prescribers rarely recommend it for jet lag.
Frequently asked questions
Why is eastward jet lag worse than westward?
Flying east means sleeping earlier than your body clock wants, which fights biology; flying west means staying up later, which the clock does far more willingly. Allow roughly a day per time zone to adapt, more when heading east.
Does melatonin work for jet lag?
Taken close to destination bedtime for eastward trips across five or more zones, it has reasonable evidence. In the UK melatonin is prescription-only, so arrange it with your GP before travelling.
Should I take zopiclone for jet lag?
Prescribers rarely recommend it — sedatives don’t shift your body clock, they just sedate you on the wrong time zone, with next-day grogginess and, on flights, prolonged immobility. Light timing is the effective tool.
How do I use light to beat jet lag?
Flying east, seek morning light and avoid late-evening light at your destination; flying west, seek evening light. Getting this backwards can push your clock the wrong way and make day three feel worse.
Questions about your sleep or your medicines? Speak to one of our pharmacists — advice is free and confidential. If you already have a prescription, you can nominate our pharmacy to dispense and deliver it.
This article is general health information based on NHS and BNF guidance. It is not medical advice, and it is not an advertisement for any medicine. Always follow your prescriber’s instructions and read the patient information leaflet. If you need urgent help call NHS 111; in an emergency call 999. [Clinical review placeholder — reviewed by NAME, Superintendent Pharmacist, GPhC reg. NUMBER, on DATE.]