Melatonin for sleep: what it does, and what it doesn't

What melatonin actually is

Melatonin is a hormone your brain makes in the pineal gland when it gets dark. Levels rise in the evening, fall around dawn, and bright light suppresses them. Its job is to tell the rest of your body what time it is, not to knock you out.

Taken at the right time, a small dose of a supplement can nudge your internal clock earlier or later. What it cannot do is override a brain that is wide awake from worry or caffeine. If you have taken melatonin and felt nothing, that is not unusual. It is a timing signal, not a sedative.

Where the evidence is reasonably good

Jet lag

A Cochrane review of trials in travellers found melatonin reduced jet lag when taken close to the target bedtime at the destination, with the clearest benefit for people crossing five or more time zones, especially flying east. Doses from 0.5 mg to 5 mg worked similarly overall, though 5 mg got people to sleep faster than 0.5 mg; doses above 5 mg were no more effective, and slow-release versions were less effective. See our guide to recovering from jet lag.

Delayed sleep phase (the extreme night owl)

Some people's body clock runs so late that they cannot fall asleep until 2 or 3 a.m., known as delayed sleep-wake phase disorder. The American Academy of Sleep Medicine (AASM) suggests strategically timed melatonin for it, a weak recommendation because the trials are small. In one trial of 116 people, 0.5 mg taken an hour before the target bedtime, plus a fixed bedtime, helped participants fall asleep about 34 minutes earlier. Protocols range from about one to five hours before the bedtime you want, so the exact timing is best set with a clinician.

Shift work

Reviews of night workers found melatonin may add roughly 24 minutes to daytime sleep after a shift, but the studies were small, low quality and inconclusive overall. Light management and scheduling matter more. See shift work and sleep for the practical side.

Where the evidence is weak: ordinary insomnia

If your problem is lying awake with a racing mind, or waking at 3 a.m. and not getting back to sleep, melatonin has little to offer. The AASM's 2017 guideline on chronic insomnia suggests that clinicians not use melatonin for sleep-onset or sleep-maintenance insomnia in adults, because there is not enough good evidence that it helps.

That does not mean you did something wrong by trying it. Insomnia is usually a problem of conditioning and arousal, and the treatment with the best evidence is cognitive behavioural therapy for insomnia (CBT-I). Our article on what insomnia is and what actually helps explains it.

Dose and timing

More is not better. Doses of 0.5 mg to 3 mg are enough to shift the clock and are a sensible starting point; higher doses add side effects without clear extra benefit above about 5 mg. Many North American products contain 5 mg or 10 mg, so start low.

• Jet lag: close to your target bedtime at the destination (roughly 10 p.m. to midnight local time), on arrival and for a few days after.
• Delayed sleep phase: a low dose in the evening, an hour or more before the bedtime you want, with a clinician settling the timing.
• Shift work: shortly before your daytime sleep period, in a dark, quiet room.

It takes an hour or two to act, so taking it at midnight after an hour of tossing and turning rarely helps.

The product may not match the label

In the US and Canada, melatonin is sold over the counter as a supplement, so it is not held to the manufacturing standards of a medicine. In the UK, by contrast, it is prescription-only.

A 2017 analysis of 31 supplements found most did not contain what the label claimed, and about one in four contained unlisted serotonin. A 2023 study of 25 gummies found 22 mislabelled, some with up to 347 percent of the stated dose. Look for independent third-party testing (in the US, the USP Verified mark), and take particular care with gummies because they look like sweets.

Safety and who should ask a doctor first

For most healthy adults, short-term use appears safe. Common side effects are headache, daytime tiredness, nausea, dizziness and irritability. Long-term safety is not well studied. In the UK, for short-term sleep problems, the NHS usually prescribes it for one to four weeks and up to 13 weeks, mainly to people aged 55 and over; for long-term insomnia it may be prescribed for longer under specialist supervision.

Some groups should talk with a doctor before using it at all:

• Children and teenagers. Melatonin is a hormone, and its long-term effects on puberty are unknown. Accidental ingestions have risen sharply: around 11,000 US emergency visits for unsupervised child ingestions from 2019 to 2022. The AASM advises storing it like any other medicine and discussing behavioural approaches with a paediatric clinician first.
• Pregnancy and breastfeeding. There is not enough safety research to say it is fine.
• People with liver or kidney problems, or an autoimmune condition such as rheumatoid arthritis, multiple sclerosis or lupus, all of which the NHS lists as reasons to check first.
• People with epilepsy, and anyone taking other medicines. Melatonin can interact with blood thinners such as warfarin, epilepsy medicines, blood-pressure medicines, some antidepressants (particularly fluvoxamine), sedatives and sleeping pills, and oestrogen-containing contraceptives or HRT; there are case reports of harm in people with epilepsy and in warfarin users. The NHS advises against alcohol with it, because the combination can make you sleep so deeply that breathing is affected; sleepy herbal remedies add to drowsiness.
• Older adults with dementia. The AASM suggests against it for the fragmented sleep-wake pattern seen in dementia, and it may linger longer in older bodies, causing daytime drowsiness.

Beyond these groups, talk with a doctor if you have used melatonin most nights for more than a few weeks, still cannot sleep, or are very sleepy in the day, snore loudly or wake gasping, because those point to a different problem, such as sleep apnea, that melatonin cannot fix.

In summary

Melatonin is a clock signal, not a sleeping pill. It has decent evidence for jet lag and for a body clock that runs late, modest evidence for shift work, and weak evidence for everyday insomnia. If you use it, keep the dose low, get the timing right, choose a tested product, and check with a doctor first if you are in one of the groups above. If sleep is still a struggle, the reliable fix is usually behavioural, not a bigger dose.