What it is good for
Jet lag — the strongest case
Melatonin helps shift the circadian clock when taken at the right local time. The evidence is best for eastward travel. Timing is critical and differs by direction, so it is worth being specific with a clinician or following a recognised protocol. See jet lag.
Delayed sleep phase
If you genuinely cannot feel sleepy until 2 or 3am, and you sleep fine once you start, you may have delayed sleep phase syndrome. Low-dose melatonin taken several hours before your current sleep time — under guidance — can advance the clock.
Shift workers and blind people with non-24-hour rhythms
Specific, clinically supervised uses with reasonable evidence.
What it is not good for
- Chronic insomnia generally. Effects are modest — typically a few minutes off sleep onset. It does not address the schedule, association and belief problems that maintain insomnia.
- Waking at 3am. Melatonin is a timing signal, not a maintenance agent. See waking up at 3am.
- Replacing sleep. It does not produce sleep; it changes when sleep is likely.
Dose and timing
Lower doses are usually better than the large amounts sold in some countries. Typical studied doses range from about 0.5 to 5 mg, taken in the evening one to two hours before target bedtime — but timing depends entirely on what you are treating, and getting it wrong can shift the clock the wrong way. Discuss it with a clinician, especially if you take other medication.
Side effects and cautions
- Generally well tolerated short-term: morning grogginess, headache, vivid dreams.
- Interactions are possible with anticoagulants, anticonvulsants, contraceptives and diabetes medication.
- Long-term safety data are limited.
- Product quality varies — supplement regulation is lax in many markets, and actual content does not always match the label.
- In pregnancy and breastfeeding, data are insufficient; discuss with your clinician.
Better first steps
For most people with insomnia, the higher-yield actions are structural: sleep restriction, stimulus control, a fixed wake time with morning daylight, and no alcohol. If your body will not settle once you are in bed, somatic work is more likely to help than a supplement.