East vs West Jet Lag: Why Is Flying East Harder?
How the direction you fly changes jet lag, why the trip home often feels worse, and how to adjust in each direction.
Part of our jet lag guide.
After a long flight: call 999 if you have chest pain or sudden breathlessness, and get urgent help for a painful, swollen calf or thigh. These can be signs of a blood clot. A fever after travelling to a malaria area needs a doctor the same day.
Key fact: Flying east shortens your day, so your body clock has to move earlier, which is harder than staying up later. That's why eastward jet lag usually lasts longer.
Flying long-haul soon?
Most jet lag gets better with the right routine. If it badly affects you, our UK prescribers can assess you online for licensed jet lag treatment. Adults 18 and over. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day.
Start Jet Lag Consultation →Why does travel direction affect jet lag?
Jet lag happens because your body clock is out of step with local time. Which way you fly decides which way your clock has to move:
- Flying east (e.g. UK to Asia, or back from the USA): local time is ahead of your body clock, so your clock has to move earlier. Doctors call this a phase advance.
- Flying west (e.g. UK to the USA): local time is behind your body clock, so your clock has to move later. This is a phase delay.
Why is flying east harder?
Most people's natural body clock runs slightly longer than 24 hours. That makes it easier to stay up later than to go to sleep earlier, which is why most people find it easier to adjust to a late night than an early morning.
Flying east gives you a shorter day. You need to fall asleep when your body still thinks it's evening or afternoon, and get up when it thinks it's the middle of the night. The CDC estimates the body clock adjusts by about 1 hour a day after flying east, compared with about 1.5 hours a day after flying west.
| Flying east | Flying west | |
|---|---|---|
| Your day | Shorter | Longer |
| Body clock must move | Earlier (advance) | Later (delay) |
| Typical problem | Can't fall asleep at night; hard to wake up | Waking very early; sleepy in the evening |
| Rough adjustment | About 1 hour a day | About 1.5 hours a day |
What happens when you fly west?
Flying west, for example to New York or Los Angeles, gives you a longer day. Staying up until a local bedtime is usually manageable, but your body clock is still ahead of local time, so you're likely to feel sleepy in the early evening and wake in the early hours of the morning for the first few days.
Why is jet lag worse coming home?
Many people find jet lag worse on the way home, especially from the USA or Canada. Coming home means flying east, which is the harder direction. You also usually go straight back to work, school and early alarms, with less flexibility to nap or sleep in, and often after a tiring overnight flight.
How your body clock adjusts
Your body clock is reset mainly by light. Light at certain times of your body's day moves the clock earlier, and at other times moves it later. Light in your body's early morning moves it earlier; light in your body's evening moves it later. That's why the timing of daylight after a flight matters so much, and why getting it at the wrong time can make jet lag last longer.
How to adjust when flying east
- Before you go: move your bedtime and wake-up time an hour earlier each day for 2 or 3 days.
- On arrival: get daylight in the morning, from a few hours after waking, and avoid bright light in the late afternoon and evening (sunglasses help).
- After 8 or more time zones east, early-morning light can push your clock the wrong way for the first couple of days, so get light from late morning instead.
- At night: go to bed at a normal local time and keep the room dark.
How to adjust when flying west
- Before you go: move your bedtime and wake-up time an hour later each day for 2 or 3 days.
- On arrival: get daylight in the afternoon and early evening, and stay up until a normal local bedtime.
- Early mornings: if you wake very early, stay in a dark room and avoid bright light for the first day or two.
For a full plan before you fly, see how to prevent jet lag. For tips once you've arrived, see how to get over jet lag, and for how long it may take, how long does jet lag last?.
Does melatonin work better flying east?
Research suggests so. A Cochrane review of 10 trials found melatonin reduced jet lag after flights across 5 or more time zones, with a larger benefit after flying east. In the UK, melatonin 3mg tablets are a prescription-only medicine licensed for jet lag in adults, taken at bedtime after you arrive. See our melatonin for jet lag guide.
Getting jet lag treatment
For an overview of jet lag, see our main jet lag guide. If jet lag badly affects you, our UK prescribers can assess adults online for licensed treatment: see our jet lag treatment page.
UK safety and reporting side effects
In the UK, melatonin is a prescription-only medicine. Melatonin 3mg tablets are licensed for the short-term treatment of jet lag in adults aged 18 and over, and they aren't licensed for jet lag in children. Before any medicine is supplied, a GPhC-registered pharmacist independent prescriber reviews your consultation, including your health and the other medicines you take. Always read the patient information leaflet in the pack.
Melatonin sold as a supplement abroad or on unregulated websites (as gummies, sprays or tablets) isn't a licensed medicine in the UK, and its strength and contents can vary. Only buy medicines from a registered UK pharmacy: you can check any online pharmacy on the GPhC register.
If you think you've had a side effect from a medicine, tell your pharmacist or doctor. You can also report it to the MHRA through the Yellow Card scheme, which helps keep medicines safe for everyone.
Jet lag is only one part of travel health. Before you go, check FCDO travel advice for your destination and TravelHealthPro for vaccines and malaria advice. Tiredness after a long-haul flight affects your reactions, so don't drive if you feel sleepy after you land.
Frequently Asked Questions
Is jet lag worse going east or west?
For most people, flying east is worse. Your body clock finds it easier to move later than earlier, and flying east means sleeping and waking earlier than your body wants to.
Why is jet lag worse coming home from America?
Coming home from the USA means flying east, the harder direction. You also often arrive after an overnight flight and go straight back to work and early alarms.
How long does it take to adjust flying east?
Roughly a day for each hour of time difference. The CDC estimates the body clock adjusts by about 1 hour a day after flying east, so a 7-hour difference may take about a week.
How long does it take to adjust flying west?
Usually a little quicker: about 1.5 hours a day. A 5-hour difference to New York often takes 3 or 4 days.
Why do I wake up at 4am after flying to the USA?
Your body clock is still on UK time, where it's already morning. Stay in a dark room until a normal wake-up time, and get daylight in the afternoon and early evening to help your clock move later.
Does flying north or south cause jet lag?
No. Jet lag comes from crossing time zones. A long north to south flight, such as the UK to South Africa, can leave you tired, but that's travel fatigue, which usually clears after a night's sleep.
References
- Centers for Disease Control and Prevention. CDC Yellow Book: Jet lag disorder. cdc.gov
- NHS. Jet lag. nhs.uk
- Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database of Systematic Reviews 2002, CD001520. cochrane.org
Medical disclaimer: This article is for information only and isn’t medical advice. Prescription medicines, including melatonin, need a clinical consultation before they can be supplied. If you have chest pain, sudden breathlessness or a painful, swollen leg after a flight, seek medical help straight away. In a medical emergency, call 999.