Melatonin
Endogenous pineal hormone sold OTC as a sleep aid and chronobiotic. Modest effect on sleep onset latency but a well-established phase-shifting agent for jet lag and circadian rhythm disorders. Very low toxicity; consumer products are frequently mislabelled for content.
01 Overview
Melatonin (N-acetyl-5-methoxytryptamine) is a hormone secreted by the pineal gland in darkness that signals biological night. As a supplement it is used both as a mild hypnotic and, more effectively, as a circadian phase-shifting agent for jet lag, delayed sleep-phase syndrome, and shift work.
Meta-analyses show a small reduction in sleep onset latency (roughly 7-12 minutes) and modest increases in total sleep time in adults with insomnia, with much larger benefit in circadian misalignment. It is not scheduled in most countries and has an exceptionally wide safety margin, but OTC products in the US are notoriously variable, with assayed content ranging from a fraction to several times the label claim.
02 Mechanism
Agonist at MT1 and MT2 melatonin receptors in the suprachiasmatic nucleus; MT1 activation promotes sleep propensity while MT2 activation mediates circadian phase shifts.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Low / physiological | 0.3–1 mg/day | Oral | Physiological doses near 0.3 mg often match or beat larger doses for sleep onset. |
| Common OTC | 1–5 mg/day | Oral | Taken 30-60 min before target bedtime; for phase advance take in the evening. |
| High | 5–10 mg/day | Oral | No consistent added hypnotic benefit; increases next-day grogginess risk. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Reduced sleep onset latencyModest shortening of time to fall asleep in adults with insomnia. | ~7-12 min faster | Clinical | |
| Circadian phase shiftingEvening dosing advances the sleep phase; effective for jet lag and delayed sleep-phase disorder. | phase shift of ~0.5-1 h/day | Clinical | |
| Improved subjective sleep qualityUsers often report deeper or more restful sleep, though objective architecture changes are small. | Observational |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Next-day drowsiness / grogginessResidual sedation the following morning, more likely with 5-10 mg doses or late-night dosing. | Mild | Common at higher doses | Clinical | |
| Vivid dreams / nightmaresSome users report unusually vivid or disturbing dreams. | Mild | Uncommon | Anecdotal | |
| Product mislabelling / inconsistent contentIndependent assays find actual melatonin content ranging from ~15% to 470% of label, with some products containing serotonin. | Moderate | Common in US OTC products | Observational |