Melatonin

Melatonin is the hormone your brain releases in the dark to signal night. As a supplement its best-supported use is shifting the body clock — above all for jet lag, where 0.5 mg and 5 mg work about equally well and more adds nothing. For ordinary insomnia it does much less, labels are unreliable, and use for a year or more has an unconfirmed link with heart failure.

For jet lag, take 0.5–5 mg of immediate-release melatonin at the destination's bedtime for three to five days. To shift your clock, use a small dose. Don't take 10 mg, don't take it every night indefinitely, and check with your doctor first if you have epilepsy or take warfarin.

What it is, and two myths about it

Melatonin is made by the pineal gland during the dark part of the day; evening light suppresses it (see Light at night).

It declines with age far less than folklore says. When 34 healthy adults aged 65 to 81 were measured under controlled conditions against 98 young men, their 24-hour average melatonin was essentially identical — 70 against 73 pmol/L — with the same night-time peak height and duration.^[1] What changes with age is usually the rhythm's timing and robustness rather than the amount.

It is probably not a direct antioxidant inside cells. A critical commentary in the field's own journal accepts that melatonin mops up free radicals in a test tube, but argues that doing so inside living tissue is neither plausible nor demonstrated. What survives is that it switches on the body's own antioxidant enzymes.^[2]

Jet lag: its best use

For travellers crossing five or more time zones, 0.5–5 mg of immediate-release melatonin taken at the destination's bedtime for three to five days helps about one person in every two treated. Doses of 0.5 and 5 mg work about equally well, though people fall asleep faster and sleep better on 5 mg; doses above 5 mg do no better, and a slow-release 2 mg product worked relatively poorly — so prolonged-release melatonin is the wrong choice here, despite its more reliable content.^[3]

Dose: small for the clock, moderate at most for sleep

About 0.3 mg restores natural blood levels, while 3 mg spills melatonin over into the following day. So for shifting the clock outside jet lag — delayed sleep timing, for example — a small dose of 0.3–1 mg, timed correctly, is the right choice; larger doses buy minutes of faster sleep at the cost of next-day effects.

For falling asleep and total sleep time, pooling 26 randomised trials, the effect peaked around 4 mg taken about three hours before bed rather than the usual half-hour.^[4] The strongest predictor of benefit was whether the person had insomnia at all, so read 4 mg as an optimum for treating insomnia, not a target for someone who sleeps well. Nothing justifies 10 mg, and bigger doses are more likely to leave you groggy.

Ordinary insomnia: a gain of minutes

For everyday insomnia the effect is small. Across 19 trials and 1,683 people, melatonin got people to sleep about seven minutes faster and added about eight minutes of sleep;^[5] an earlier analysis of 17 trials found about four minutes faster and thirteen minutes more.^[6] The American Academy of Sleep Medicine's guideline on sleep drugs recommends, conditionally, against melatonin for insomnia in adults.^[7] In Europe a prolonged-release prescription form (2 mg) is licensed for insomnia in adults aged 55 and over, for up to three months.^[8] That case is strongest in older adults, but not because they lack melatonin (see above). For chronic insomnia, cognitive behavioural therapy is the treatment that works; see Treating chronic insomnia.

Body-clock disorders and shift work

Someone who reliably cannot fall asleep before 03:00 may have delayed sleep-wake phase disorder; an older adult asleep by 19:00 and awake at 03:00 may have its mirror image. Both are diagnosable conditions. The American Academy of Sleep Medicine's guideline endorses timed melatonin for the delayed form, and timed light for the advanced form.^[9] The guideline does not cover shift work; for night-shift workers, timed melatonin is commonly suggested alongside a blacked-out bedroom for daytime sleep, but this page has no trial evidence for it.

Labels are unreliable

Over-the-counter melatonin often contains a very different amount from the label. One analysis found content from 83% below to 478% above the stated dose, with batches of a single product differing by up to 465%; more than 71% missed their label by over 10%, and eight of the 31 products contained serotonin.^[10] Gummies, the format most people now buy, are no better: among 25 tested, contents ran from 74% to 347% of the label, 88% were inaccurately labelled, and one contained no melatonin at all but 31.3 mg of CBD. No serotonin turned up in the gummies.^[11] The problem has not improved: a US Food and Drug Administration survey of 110 melatonin products marketed for children found it in 108 of them, at anywhere from 0% to 667% of the declared amount.^[12]

Long-term use: a warning, not a verdict

A 2025 conference report linked melatonin prescribed for insomnia for a year or more to roughly double the rates of heart failure and death.^[13] It compared about 65,000 long-term users with matched non-users: over five years, heart failure showed up in about 4.6% of users against 2.7%, and death in about 7.8% against 4.3%.^[14]

It does not prove harm:

It is a conference abstract, not a peer-reviewed paper, with no dose data.
It is observational: long-term users tend to have worse insomnia, more depression and unrecorded use of other sleep drugs, any of which could explain it.^[15]
It mixed countries where melatonin is prescription-only with ones where it is sold over the counter, so anyone buying it off the shelf counted as a non-user.

But it is large enough to argue against calling indefinite nightly use harmless. Occasional low-dose use remains well supported.

Beyond sleep

In one trial, 5 mg of melatonin worsened glucose tolerance, but only in carriers of a common variant of the melatonin-receptor gene MTNR1B.^[16] Across 31 trials, melatonin slightly improved markers of insulin resistance, so this is a caveat for one group, not a general metabolic harm.^[17] In menopausal women, two small trials hinted at better bone density — too different to pool, and often combined with other ingredients — with no clear effect on anxiety or menopausal symptoms.^[18] The anti-ageing case rests on its role as an antioxidant in mitochondria, which is theory, not evidence.^[19]

Who should be careful

Older people with dementia. The sleep-medicine guideline recommends against melatonin for sleep problems in this group; timed light is the endorsed option.^[20]
People with epilepsy or taking warfarin. The jet-lag review flagged possible harm in both groups.^[21]

What to do

Use it for jet lag: 0.5–5 mg immediate-release at the destination's bedtime for three to five days, when crossing five or more time zones.
For delayed sleep timing, keep it small (0.3–1 mg); never go above 5 mg, and never 10 mg.
For ordinary insomnia, expect minutes, not hours, and look at cognitive behavioural therapy first.
Treat the label dose as approximate, given how far products drift from it.
Don't take it every night indefinitely, and see a sleep specialist if your schedule won't move.

See Sleep supplements for how melatonin compares with other sleep aids, and Circadian rhythms for light and timing.