Melatonin, what it is actually for

Melatonin is a timing signal, not a sedative. It is well supported for shifting your clock — jet lag, shift work, early-stage circadian rhythm disorders — and much less convincingly supported as a nightly aid for ordinary insomnia in someone whose clock is already roughly where it should be.

Why this works, and where it stops working

Your body already produces melatonin every evening as part of the same light-driven system covered in the daylight and wake-time articles. It rises as it gets dark and signals to the rest of the body that night has started. That is a timing cue, distinct from the sedation produced by something like an antihistamine or alcohol.

This is exactly why the evidence looks the way it does. For jet lag, where the problem genuinely is a clock in the wrong place, trials and systematic reviews show a fairly consistent benefit for how quickly people adjust. For ordinary insomnia in someone whose clock is not obviously displaced, meta-analyses generally find a real but small effect on falling asleep faster — often only several minutes — with much more mixed results on total sleep time or how rested people feel. It is being used, in that second case, for a problem it was not really designed to solve.

There is a practical complication on top of the science: melatonin sold over the counter is regulated very differently between countries, and independent testing has repeatedly found that labelled doses do not reliably match what is actually in the product. That uncertainty is baked into the grade here as much as the mixed trial results are.

How to use it well

1. For jet lag or shift work, take a low dose, generally in the 0.5–3mg range research most often uses, timed for the bedtime of your destination or new schedule, starting a day or two before the shift if possible.
2. For ordinary insomnia, try the free structural changes — wake time, morning light, caffeine cut-off — before reaching for this. They address the same system with a much stronger evidence base and no interaction risk.
3. Take it thirty to sixty minutes before the target bedtime, not right at the moment you get into bed. As a timing signal it needs a short lead time to act.
4. Lower is generally better than higher. Doses well above what trials use are common on shelves and are not shown to work better; they mainly increase the odds of grogginess the next morning.
5. Buy from a source with third-party testing where that is available, given the labelling problem above.

Common mistakes

• Using it nightly as a sleep aid for years. This is the least-supported use case and the one it is most commonly sold for.
• Taking a high dose right at bedtime and expecting fast sedation. That is treating it like a sedative, which is not what the mechanism is.
• Not checking interactions. This is the one supplement on this site where a pharmacist conversation is worth having before you start, not after something goes wrong.
• Blaming melatonin when the clock is the real problem. If wake time is drifting all over the week, no amount of an evening supplement will out-compete that.

What should change

For a genuine circadian shift — a flight across time zones, a new shift schedule — expect noticeably faster adjustment within a few days. For ordinary insomnia, expect at most a modest reduction in how long it takes to fall asleep, and do not expect it to fix fragmented or unrefreshing sleep on its own.

Your next step

If insomnia persists after the free changes and this have both been tried honestly, that is the point to bring it to a doctor rather than to try further supplements alone.