Melatonin: Small, Real, and Usually Mistimed
Melatonin's effect on falling asleep is small but real, and timing matters more than dose.
Evidence suggests exogenous melatonin shortens the time taken to fall asleep by a few minutes and adds a small amount of total sleep time. The larger point is that it works as a clock signal rather than as a sedative: a dose-response meta-analysis found benefit peaking around 4 mg with timing relative to your own circadian phase the significant predictor, which is why taking more at bedtime is the common mistake. We grade this B because the effect sizes are small and because the reviews behind them have been rated low in methodological rigour despite their number.
- Misconception: 'More melatonin works better.' Benefit plateaus around 4 mg; timing is the stronger predictor.
- Misconception: 'It is a sedative.' It shifts circadian timing rather than inducing sleep directly.
- Does not recommend, dose or endorse melatonin or any supplement
- Does not advise on starting, changing or stopping any medication
- Considering any sleep supplement → pharmacist or clinician, particularly alongside other medication
Every source below carries its own grade and links to the original study. This is the audit trail.