Melatonin is the supplement people reach for when sleep goes wrong, and it is also widely misunderstood. Melatonin is a hormone your brain’s pineal gland releases in the evening as light fades. Its job is to signal darkness and timing to the body clock — it tells your system when to sleep more than it forces sleep itself. That distinction explains both where supplements genuinely help and where the evidence is disappointing.
Regulation varies by country: melatonin is sold as a dietary supplement in the United States, while in the United Kingdom and much of Europe it is a prescription medicine, usually in prolonged-release form for older adults with insomnia. That difference alone hints that authorities view it as a drug with specific uses, not a benign vitamin.
Where the evidence is reasonably good
The clearest use is jet lag, particularly travelling east across five or more time zones, where melatonin taken at the destination’s evening can reduce symptoms. It is also used, with supporting evidence, for certain circadian rhythm disorders — for example delayed sleep phase, where people cannot fall asleep until very late, and non-24-hour rhythm disorder in people who are totally blind. In these cases melatonin works as a clock-setting signal, and timing relative to your current rhythm matters as much as dose.
For ordinary chronic insomnia, meta-analyses find melatonin shortens the time to fall asleep by only a few to several minutes on average — a real but small effect, much weaker than cognitive behavioural therapy for insomnia (CBT-I), which guidelines recommend as first-line treatment.
Dose and timing: less, earlier
Supplement doses commonly sold — 5 or 10 mg — are far above what the body produces and above the doses used in many studies. Low doses around 0.5-1 mg often shift the clock as effectively as high ones, with less next-morning grogginess. For circadian purposes, melatonin is typically taken some hours before the desired sleep time rather than at bedside, but the correct timing depends on the problem being treated, which is why rhythm disorders are best handled with professional guidance.
Product quality is another caveat: an analysis of melatonin supplements published in the Journal of Clinical Sleep Medicine found actual content ranging from far below to several times the labelled dose, with serotonin contamination in some products. Where regulated or pharmacy-grade products are available, they are the safer choice.
Safety and interactions
Short-term use is generally well tolerated; reported effects include morning sleepiness, vivid dreams, headache and dizziness. Melatonin can interact with medicines including some anticoagulants, blood-pressure drugs, immunosuppressants and sedatives, and evidence in pregnancy and childhood is limited — long-term use in children in particular should be clinician-led. It can also impair driving if taken too late or at high dose.
Practical takeaways
Think of melatonin as a clock tool, not a knockout drop. It is most defensible for jet lag and diagnosed rhythm problems, at low doses, timed deliberately. For persistent insomnia, invest first in the approaches with stronger evidence — regular wake times, morning light, and CBT-I — and discuss supplements with your clinician or pharmacist, especially if you take other medicines. If you do use it, choose a regulated product, start low, and stop if it leaves you groggy, since that usually signals the dose or timing is wrong.
