For short-term jet lag use, melatonin is generally considered safe and well tolerated in most healthy adults — but "generally safe" isn't "safe for everyone", which is exactly why it's a prescription medicine in the UK rather than a supplement off a shelf. Here's what to know before you fly: the real (mild) side effects, who should be cautious, and why UK regulation actually works in your favour.
The reassuring part
Used occasionally, at sensible doses, for the few days around long-haul travel, melatonin has a good safety record. It's a version of a hormone your own body makes nightly, it isn't habit-forming in the way sedative sleeping tablets can be, and jet lag is one of its best-studied and most-supported uses. For a healthy adult taking it for a short adjustment window, the risk profile is low. That's the headline — with important asterisks below.
Possible side effects
Usually mild and short-lived when they occur:
- Daytime drowsiness or grogginess — the most common, especially with higher doses or mistimed dosing
- Headache
- Dizziness
- Nausea
- Occasionally vivid dreams, or short-lived low mood/irritability
Because drowsiness is possible, don't drive or do anything needing full alertness until you know how it affects you — including after you take it on arrival.
Who should be cautious or avoid it
This is the heart of why a clinician checks first. Melatonin may not be suitable, or needs specific caution, if you:
- Are pregnant or breastfeeding — not recommended, as safety isn't established
- Have an autoimmune condition — melatonin interacts with immune signalling and is generally advised against
- Have epilepsy or a seizure disorder — needs specialist input
- Have liver or kidney problems — these affect how the medicine is cleared
- Have diabetes — it can affect blood sugar and needs consideration
- Have a history of depression or other mood disorders — worth discussing first
Melatonin is also not routinely recommended for children for jet lag without specialist advice, and older adults may be more sensitive to next-day grogginess.
Interactions worth flagging
Melatonin can interact with several common medicines — including blood thinners (such as warfarin), anti-epileptic drugs, some diabetes medicines, sedatives and other sleep aids (additive drowsiness), immunosuppressants, and certain antidepressants. This is why "what else do you take?" is a core consultation question, not a formality. Combining melatonin with alcohol is also best avoided — the drowsiness stacks and the sleep quality suffers.
Why UK prescription status is a feature, not a hassle
In the US, melatonin sits on supermarket shelves as a food supplement — which sounds convenient until you learn that unregulated melatonin products have repeatedly been found to contain wildly different amounts than the label claims, sometimes several times more. In the UK it's a licensed prescription medicine, meaning the dose is what the box says, the quality is controlled, and a clinician has checked it's appropriate for you and your other medicines. The trade-off is you must arrange it before you travel — but you get a product you can actually trust and advice tailored to you.
The sensible summary
For a healthy adult, short-term melatonin for a long-haul trip is a low-risk, well-evidenced way to ease jet lag — provided it's the right fit for your health and medicines, taken correctly for your direction of travel (see timing guide), and sourced properly. The five-minute assessment that confirms all of that is the point of a travel consultation — and it's what turns "generally safe" into "safe for you".
Frequently asked questions
Is melatonin safe to take for jet lag?
For most healthy adults using it short-term around long-haul travel, yes — it's well tolerated with mainly mild side effects. It isn't suitable for everyone, which is why a clinician checks first in the UK.
What are the side effects of melatonin?
Most commonly daytime drowsiness, headache, dizziness or nausea — usually mild and short-lived. Don't drive until you know how it affects you.
Who shouldn't take melatonin?
Caution or avoidance applies in pregnancy and breastfeeding, autoimmune conditions, epilepsy, liver or kidney problems, diabetes, and some mood disorders — and it interacts with several common medicines. A consultation screens for these.
Why can't I just buy melatonin like in America?
It's a prescription-only medicine in the UK, so dose and quality are regulated — US supplements have been found to be frequently mislabelled. Arrange it before you fly rather than buying it abroad.
References
- British National Formulary. Melatonin — cautions, interactions, side effects. bnf.nice.org.uk.
- Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev. 2002;(2):CD001520.
- Erland LAE, Saxena PK. Melatonin natural health products and supplements: presence of serotonin and significant variability of melatonin content. J Clin Sleep Med. 2017;13(2):275–281.
- NHS. Melatonin. nhs.uk/medicines/melatonin.