Melatonin

Is melatonin safe?

For adults using it for a few nights or weeks, such as for jet lag, melatonin is one of the lower-risk sleep aids. The NIH's complementary medicine centre lists headache, dizziness, nausea and sleepiness as the usual side effects, and there is no credible pattern of liver or kidney damage.

The problems are elsewhere. In the US it is sold as a supplement, with doses that often differ from the label, in sweet gummies that small children find and eat. It interacts with several common medicines. And nobody knows much about taking it every night for years.

That last gap drew attention in November 2025, when an observational study of health records presented at the American Heart Association's annual meeting looked at more than 130,000 adults with insomnia. Those recorded as using melatonin for a year or more were diagnosed with heart failure more often over five years (4.6% against 2.7%). It was a meeting abstract, not peer-reviewed, could not separate melatonin from the poor sleep it was taken for, and in some countries in the data melatonin is prescribed, so heavier users may simply have been sicker. A 2026 analysis of US national survey data in Open Heart found no significant link between recent melatonin use and heart failure. It is a reason for caution about indefinite use, not proof of harm.

What is in the bottle

Melatonin is a hormone, and doses matter. That makes label accuracy more important than for most supplements, and testing keeps finding gaps.

In 2023, a research letter in JAMA by Pieter Cohen and colleagues tested 25 melatonin gummy brands bought in the US. Only three were within 10% of the stated dose. The actual amount ranged from 74% to 347% of the label, or 1.3 to 13.1 mg per serving. One product contained no melatonin, only CBD. Industry groups said the study applied drug standards to supplements and that overages are allowed to keep products in date. That is true, but it means a parent following the label cannot know the dose.

An earlier Canadian study (2017) found melatonin content from 83% below to 478% above the label, and 26% of products contained serotonin, a related compound that is not supposed to be there.

Mix-ups also happen at the factory. The FDA's enforcement database lists melatonin bottles that turned out to hold other supplements (2015, 2019 and 2021 recalls) and, in 2026, magnesium glycinate gummies recalled because they contained melatonin that was not on the label.

Where melatonin is a licensed medicine, such as the 2 mg prolonged-release tablet prescribed in the UK, doses are tightly controlled. In the US, look for the USP VerifiedThird-party testingTesting of a supplement by an independent lab to check that it contains what the label says and is free of set contaminants.More in the glossary mark, which few melatonin products carry, and prefer plain tablets to gummies.

Children and accidental poisoning

The CDC counted 260,435 reports of children swallowing melatonin in 2012 to 2021, up 530% over the decade. By 2021, melatonin accounted for 4.9% of all paediatric calls to US poison centres. Most children (84%) had no symptoms. But 4,097 were admitted to hospital, 287 needed intensive care, five needed a ventilator and two children under 2 died.

If you keep melatonin at home with young children, store it in a locked cupboard, not on the bedside table.

Interactions

Melatonin is broken down mainly by the liver enzyme CYP1A2CYP450 enzymesA family of liver enzymes that break down many medicines. When another drug or supplement speeds them up or slows them down, drug levels change.More in the glossary. Anything that blocks that enzyme raises melatonin levels:

• Fluvoxamine, an antidepressant, raised melatonin exposure 17-fold (and peak levels 12-fold) according to the EU label of the licensed 2 mg tablet. Other SSRIs such as sertraline have less effect, but ask a pharmacist.
• Quinolone antibiotics and cimetidine also slow its breakdown, while carbamazepine and rifampicin speed it up.
• Sedatives, sleeping pills, opioids and alcohol add to drowsiness.
• Warfarin and other blood thinners: there are reports of changed INR, and the NIH advises supervision.
• Epilepsy medicines, diabetes medicines and immunosuppressants may be affected.
• Oral contraceptives and hormone replacement (oestrogens) raise melatonin levels.

Combining melatonin with other sedating supplements such as kava or ashwagandha increases next-day drowsiness.

Who should talk to a doctor first

• Pregnant or breastfeeding women. There is little safety research.
• People with epilepsy, depression or an autoimmune disease.
• Anyone taking the medicines listed above.
• Parents considering it for a child.
• Anyone who has been taking it nightly for more than a few weeks.

How to use it more safely

Use the smallest dose that works. For jet lag, 0.5 to 5 mg near bedtime at your destination is the range used in trials. Do not drive or use machinery for several hours after a dose. Prefer a product carrying the USP VerifiedThird-party testingTesting of a supplement by an independent lab to check that it contains what the label says and is free of set contaminants.More in the glossary mark, and in countries where it is a medicine, use the licensed version from a pharmacy.

How we scored it

Melatonin does well on organ toxicity (88) and dose safety (82). Product quality (58) is its weakest factor because of repeated findings of wrong doses and contamination in US products. Interactions (72) and regulation (66) are mid-range: several medicines matter, and many countries treat melatonin as a prescription drug. For a sleep aid with a different profile, see magnesium.