Melatonin improves sleep

Melatonin helps some sleep problems much more than others. The clearest benefit is for jet lag: in a Cochrane review of 10 trials, eight found that melatonin taken close to bedtime at the destination reduced jet lag after flights across five or more time zones. For ordinary trouble falling or staying asleep, the effect is small. A 2023 review of trials in adults with diagnosed insomnia found that a prolonged-release form of melatonin shortened the time to fall asleep by about 5 to 6 minutes compared with placebo. The largest analysis of sleeping medicines, covering 154 double-blind trials in 2022, found that melatonin did not clearly improve how people with insomnia rated their sleep, and its authors rated their confidence in the melatonin results as very low. For shift work, a Cochrane review found that melatonin taken after a night shift added about 24 minutes of daytime sleep, and rated that evidence low quality.

The 2023 European insomnia guideline does not recommend fast-release melatonin for insomnia, citing a lack of evidence that it works, except where the body clock is part of the problem, and says a prolonged-release prescription form can be used for up to three months in people aged 55 and over. Two US guidelines on chronic insomnia, from the American Academy of Sleep Medicine in 2017 and the American College of Physicians in 2016, found too little strong evidence on melatonin's effectiveness or safety to recommend it. The physicians' guideline strongly recommends cognitive behavioral therapy for insomnia as the first treatment, and so does the European guideline.

Dose and timing may matter, though the evidence here is indirect. A 2024 analysis of 26 double-blind trials, most of them run in healthy volunteers for a night to a few weeks, found melatonin cut the time to fall asleep by about 9 minutes and added about 20 minutes of sleep compared with placebo, with a smaller effect on falling asleep in people with insomnia than in good sleepers. Across those trials the benefit rose with dose up to about 4mg and did not grow beyond that, and trials that gave melatonin 2 to 3 hours before bedtime saw a larger drop in the time to fall asleep than trials that gave it at bedtime. The authors' model predicted little benefit from the schedule most often used in clinical practice, 2mg taken 30 minutes before bed. They describe these patterns as predictions from comparing trials that each used one schedule, which still need testing directly, and note that even the best predicted effect was less than half of what cognitive behavioral therapy achieves for falling asleep.

Reported side effects are few, mainly daytime sleepiness, dizziness, headache and nausea, and the US government's drug-induced liver injury database rates melatonin an unlikely cause of liver damage. The largest long trial gave 791 adults with insomnia a 2 mg slow-release tablet nightly for up to six months and found adverse events no more common than on placebo. A few smaller trials ran longer: in a one-year trial in 81 postmenopausal women, adverse events and falls were as frequent on placebo as on melatonin, and in a trial lasting up to three and a half years in 189 care home residents, most with dementia, side-effect ratings did not rise but mood was rated worse on melatonin. For use over many years the evidence is observational, which cannot separate melatonin from the reasons people take it. The NIH's complementary health center notes that melatonin may interact with epilepsy and blood-thinning medicines, there is little research on use during pregnancy or breastfeeding, and in older people it can stay active longer and cause next-day drowsiness.

In the US melatonin is sold as a dietary supplement rather than an approved drug, while in several other countries it is prescription-only. What is in the bottle does not always match the label. A 2017 test of 31 products found that most did not contain the amount listed, and about a quarter contained serotonin, a hormone that can be harmful even at low levels. A 2023 test of 25 gummy products found 22 mislabeled, most holding more melatonin than stated and some up to about three and a half times as much. The European insomnia guideline also notes that melatonin bought in shops and online varies in quality. The CDC estimated about 11,000 emergency department visits from 2019 to 2022 for children aged 5 and under who swallowed melatonin unsupervised, many involving flavored products such as gummies.