Melatonin: does it work, and how to take it

Does melatonin work?

Yes — with important caveats about what it works for, and how to get it legally in the UK. Melatonin earns a Grade A rating for jet lag and circadian disruption, and a solid Grade B for reducing the time it takes to fall asleep. It is not a sedative. It is a circadian signal — your brain's way of saying "it is now dark, wind down" — and that distinction changes everything about how and when to use it.

For jet lag, the evidence is as clear as it gets in sleep science. A 2019 meta-analysis published in the Journal of Pineal Research established that dose and timing of melatonin are the primary drivers of efficacy — and that getting the timing wrong can actively worsen circadian misalignment. For general sleep-onset (falling asleep faster), a pooled analysis of randomised controlled trials found an average reduction of approximately 7 minutes. Modest, but consistent — and meaningful if you are regularly staring at the ceiling at 11 pm when you should be asleep by 10.

What melatonin actually is

Melatonin is a hormone produced by the pineal gland in response to darkness. Its rise in the evening signals the start of the biological night, lowering core body temperature and priming the body for sleep. Crucially, it does not knock you out — it repositions your sleep window. This is why it is uniquely effective for circadian disruption (jet lag, shift work, delayed sleep phase) and less impressive for someone with chronic insomnia driven by anxiety, pain or poor sleep hygiene.

In the UK, melatonin is classified as a prescription-only medicine (POM). The licensed preparation — Circadin 2 mg prolonged-release — is approved for short-term treatment of primary insomnia in adults aged 55 and over. Other formulations and uses exist but require a prescriber's authorisation. Products sold freely online or in health shops are not legally authorised for sale in the UK and may be misdosed or contaminated. Obtain melatonin via your GP or a UK-regulated online pharmacy only.

The evidence — benefit by benefit

Jet lag and circadian disruption (Grade A). This is melatonin's headline act. Multiple RCTs and systematic reviews confirm it reduces jet-lag severity, accelerates re-synchronisation after transmeridian travel, and shortens the time to return to normal sleep-wake cycles. Eastward travel (which requires phase advance) typically benefits more than westward. Shift workers also show meaningful improvement in daytime sleep quality and subjective alertness when melatonin is timed correctly to the new sleep window.

Sleep-onset latency (Grade B). For people without circadian disruption, melatonin's effect on falling asleep is real but modest — roughly 7 minutes faster on average across pooled data. This is clinically meaningful for some, marginal for others. If your sleep problem is not primarily about when you sleep but about sleep quality or staying asleep, melatonin is less likely to be the lever you are looking for. Magnesium glycinate or ashwagandha may be more appropriate for stress-driven poor sleep.

Insomnia in adults over 55 (Grade B). This is the licensed UK indication. Circadin 2 mg is approved for short-term use in this group and has demonstrated improvements in sleep quality and morning alertness compared to placebo, without the dependency risks associated with hypnotics.

How to take melatonin

Dose matters less than timing. Research supports a range of 0.5–5 mg, taken 30–60 minutes before the target sleep time (not your current bedtime, but where you want your sleep to be). Starting at the lower end — 0.5–1 mg — is wise; many people find it sufficient, and higher doses increase the risk of next-day grogginess without adding proportionate benefit.

For jet lag specifically: begin taking melatonin on the first night at your destination, at local bedtime. Continue for 2–4 nights until circadian alignment is restored. Avoid taking it mid-afternoon in the destination time zone — you will reinforce the wrong phase.

For shift workers: take melatonin shortly before your intended daytime or irregular sleep window, not reflexively at 10 pm if that is not your target sleep time.

Form: In the UK, the legally available form is the GP-prescribed Circadin 2 mg (prolonged-release). Do not crush or split prolonged-release tablets.

Who should take melatonin — and who should not

Most likely to benefit:

• Frequent travellers crossing multiple time zones
• Shift workers trying to sleep at non-standard hours
• Adults over 55 with difficulty initiating sleep (under GP supervision)
• Anyone with delayed sleep phase (chronically going to sleep much later than desired)

Who should avoid it or seek medical advice first:

• Pregnant or breastfeeding women (insufficient safety data)
• Under-18s (except under specialist supervision — paediatric sleep medicine)
• Anyone on anticoagulants (increased bleeding risk), anticonvulsants, immunosuppressants, or diabetes medication (glucose regulation may be affected)
• People with autoimmune conditions — melatonin has immunomodulatory properties

Safety and interactions

At doses used therapeutically (0.5–5 mg), melatonin has a good short-term safety profile. The most common complaint is next-day grogginess — a direct consequence of taking too high a dose or taking it too early in the evening. Vivid or unusual dreams are also reported. There is no robust evidence of physical dependence or withdrawal, but using any sleep aid without addressing underlying causes of poor sleep is a short-term strategy at best.

The key drug interactions to be aware of:

• Anticoagulants (e.g. warfarin): melatonin may enhance anticoagulant effect — always inform your GP
• Anticonvulsants: pharmacodynamic interactions possible — specialist supervision required
• Immunosuppressants (e.g. ciclosporin): melatonin's immunomodulatory effects may interfere
• Diabetes medications: some evidence melatonin affects insulin secretion — glucose monitoring advisable

General information only — not medical advice. Always consult a GP or pharmacist before starting, especially if pregnant, breastfeeding, under 18, or on any regular medication.

How to get melatonin in the UK

This is the single most important practical point on this page: melatonin is a prescription-only medicine in the UK. You cannot legally buy it over the counter in a UK pharmacy or health shop. Products sold on some UK websites or imported from the US are not authorised and may be inaccurately dosed (US OTC products range from 0.5 mg to 20 mg — a 40-fold variation).

Your options:

1. GP prescription — appropriate for insomnia (over-55s) or documented circadian disorder
2. Regulated UK online pharmacy with prescribing service — legitimate, convenient for jet lag, typically involves a short questionnaire reviewed by a prescriber
3. Travel medicine clinics — often have fast access for frequent flyers

Avoid grey-market imports. Purity, dose accuracy and contamination are real concerns with unregulated products.

The verdict

Melatonin is the supplement with the clearest evidence for jet lag and circadian disruption — Grade A, no serious competition. For falling asleep faster in general, Grade B evidence supports a real but modest benefit (~7 minutes). It is not a magic sleep pill, and it is not a sedative. Used correctly — right dose, right timing, right source — it is genuinely useful. Used wrong (high dose, wrong time, unregulated product), it can worsen sleep and cause next-day fog.

That said, supplements — including melatonin — are roughly 5% of the result. Sleep architecture, training load, stress management, nutrition and recovery together account for the other 95%. If your sleep is consistently poor, the answer is rarely a supplement. Book a free consultation — a coach who understands how training, nutrition and recovery interact will get you to the root of it far faster than any pill. Or start with our free Blueprint quiz to understand where your biggest gains are hiding.

For context on how melatonin compares to magnesium glycinate for general sleep support — especially if you are not dealing with jet lag — see our head-to-head comparison on the differences in mechanism, evidence and UK accessibility.