Melatonin helps bring forward the moment you fall asleep and resets your body clock when you cross time zones, but it is not a sedative that keeps you asleep all night. Taken close to bedtime, at the right dose and time, it can shorten how long it takes you to drop off. Taken at the wrong time or dose, it simply doesn’t do much, or leaves you groggy the next day.
What it is and what it really does
Melatonin is a hormone your own brain produces, in the pineal gland, in response to darkness. It is the biological signal that marks the start of the night and helps synchronise your circadian rhythm, the internal 24-hour clock that governs when you feel sleepy and when you are awake. Light, especially from screens at night, slows its natural production.
As a supplement, melatonin does not work like a classic sleeping pill that switches off the nervous system. It works as a time signal: it tells your body “it’s night now”, which is why the effect depends a great deal on when you take it, not just how much.
For sleep: what to expect and what not to
The European Food Safety Authority (EFSA) has endorsed that taking 1 mg of melatonin close to bedtime contributes to reducing the time it takes to fall asleep, based on several meta-analyses of controlled studies. That is the best-demonstrated effect: it helps you get to sleep sooner, not necessarily to sleep more hours in a row or to avoid waking in the night.
For chronic insomnia, meaning when the problem lasts a month or more, the evidence is considerably weaker. Institutions such as the US National Center for Complementary and Integrative Health (NCCIH), part of the NIH, point out that the main clinical guidelines do not find strong enough evidence to recommend melatonin as a treatment for chronic insomnia, and put cognitive behavioural therapy first. If you have been sleeping badly for weeks, melatonin may not be the real solution.
For jet lag: here there is room
Jet lag is where melatonin has its clearest role. EFSA also endorses that low doses, from 0.5 mg, taken close to bedtime at your destination, help relieve the subjective feeling of jet lag after flights that cross several time zones. Independent scientific reviews confirm that it reduces symptoms such as daytime tiredness and the digestive discomfort associated with jet lag, on both eastbound and westbound flights, although the size of the effect is moderate.
Supplement or medicine: the 1.9 mg line
In Spain this boundary matters because it changes where and how you can buy it:
| Format | Usual dose | Where it is sold |
|---|---|---|
| Food supplement | Up to 1.9 mg per dose | Pharmacies and health shops, without prescription |
| Medicine | 2 mg or more | Pharmacies only, some on prescription |
The Spanish Agency for Food Safety and Nutrition (AESAN) clarified that, under mutual recognition within the European Union, supplements with less than 2 mg of melatonin per daily dose can be sold in Spain as foods. Above that amount, the product has to be authorised as a medicine by the AEMPS, Spain’s medicines agency, with product information that sets the indication, maximum dose and length of treatment, and some presentations require a prescription. If you’re not sure what you have in front of you, the pack tells you: one says food supplement and the other carries a registration number as a medicine.
How and when to take it
Timing matters more than it seems. Taking it too early or too late relative to your usual bedtime may not bring your sleep forward or may even shift it in the opposite direction.
| Goal | When to take it | Reference |
|---|---|---|
| Falling asleep | 30 minutes to 2 hours before bed | NCCIH / EFSA |
| Jet lag | Close to bedtime at your destination, for the first few days | EFSA |
| Ongoing use | Not recommended to continue without a review | AEMPS product information |
Prolonged-release presentations authorised as medicines are taken after eating something, not on an empty stomach, because food changes how they are absorbed.
Side effects and who should avoid it or ask first
In the short term and at usual doses, the effects described are generally mild: headache, dizziness, lingering drowsiness the next day or digestive discomfort. Some groups should be careful:
- If you take anticoagulants (warfarin or the so-called direct-acting ones), melatonin can increase their effect; ask before combining them.
- If you have epilepsy, medical supervision is recommended because it can interact with your treatment.
- It is not recommended in pregnancy or while breastfeeding, because there is not enough data to confirm it is safe at those times.
- In older people, melatonin can stay active in the body for longer and cause daytime drowsiness.
Children and teenagers
It is not a supplement to give children on your own initiative. Guidelines agree that its use in children should be assessed by a healthcare professional, because data on the best long-term dose are lacking and because, as a hormone, there is a theoretical concern that it could interfere with hormonal development. Always keep tablets, and especially gummy formats, out of children’s reach: accidental ingestion is a common reason for calls to poison services.
When to see a doctor
- You have been sleeping badly for more than three or four weeks, with or without melatonin.
- You wake up several times in the night or struggle to stay asleep, rather than to fall asleep.
- You take anticoagulants, have epilepsy, are pregnant or are breastfeeding.
- You notice severe drowsiness the next day, a persistent headache or any reaction that doesn’t improve when you adjust the dose or timing.
- You want to give it to a child.
This article is for information only and does not replace an assessment by a healthcare professional. Sources: AEMPS-CIMA, summary of product characteristics for melatonin, AESAN, update on melatonin in food supplements, EFSA Journal, opinion on melatonin and reduction of sleep onset latency, EFSA Journal, opinion on melatonin and jet lag, NCCIH-NIH, Melatonin: What You Need To Know.