Melatonin: What It Actually Does, the Doses Studied, and Why Most Products Have 10× Too Much

Educational journalism, not medical advice. Every claim here is checked against its cited sources by editor Timothy Bunce — a health writer, not a physician. It isn’t specific to your situation: for health decisions, talk to your own clinician. How we work →

Some links in this article are affiliate links. If you buy through one, The Beachside Reader earns a commission at no extra cost to you. It never changes which products we pick, or what we say about them. Full affiliate disclosure →

What melatonin actually does

Melatonin is a hormone produced by the pineal gland, secretion rising in the evening as ambient light drops and peaking in the middle of the night. Its primary role is signalling the timing of biological night to every cell in the body — not producing sleep directly. The sleepiness people associate with melatonin is downstream of this timing signal, not the primary effect.

This distinction explains the trial results. Melatonin produces:

• Modest reduction in sleep latency — 7-12 minutes faster onset in meta-analyses.
• Strong effects on circadian phase shifting — useful for jet lag and shift-work adjustment.
• Small effects on total sleep time — 8-15 additional minutes per night on average Ferracioli-Oda 2013.
• Strong effects on delayed sleep phase syndrome — people whose body clocks are shifted late.

Why more isn’t better: 0.3mg vs 3-10mg

In dose studies, about 0.3mg taken by mouth produced blood levels close to the body’s natural night-time peak. Higher doses produce supraphysiological levels — concentrations many times higher than the body produces naturally. Two possible problems follow:

• Receptor desensitisation: laboratory and animal research suggests chronically elevated melatonin can desensitise its receptors. Whether this makes high doses less effective over weeks of use in people hasn’t been firmly established.
• Persistent next-morning levels: high doses may not clear by morning. In the trial below, 3mg left melatonin elevated into daylight hours, which may contribute to the grogginess or “hangover” some people report.

A landmark trial in older adults with age-related insomnia tested 0.1mg, 0.3mg, and 3.0mg doses against placebo: the 0.3mg dose — which raises blood melatonin to the level the body produces naturally at night — restored sleep efficiency, while the 3.0mg dose left melatonin circulating into daylight hours and induced hypothermia, with no added sleep benefit over the 0.3mg dose Zhdanova 2001. The 3-10mg products that dominate the retail shelf contain roughly 10-30 times the 0.3mg dose that performed best in that trial.

Timing matters

For circadian problems, timing matters as much as dose: melatonin shifts the body clock in different directions depending on when it’s taken, and taken at the wrong time it can shift the clock the wrong way. What the research covers:

• For trouble falling asleep: trials have generally given melatonin shortly before the intended bedtime, and the average effect is modest (see above). Trouble falling asleep that lasts for weeks is worth raising with your doctor.
• For circadian phase delay (you can’t get to sleep until 3am despite trying earlier): studies time melatonin several hours before a person’s natural sleep onset, and the window is individual. Because mistimed melatonin can push the clock the wrong way, delayed sleep phase is best assessed and managed with a clinician or sleep specialist.
• For jet lag eastward: trials have typically given melatonin close to bedtime at the destination for a few nights. A pharmacist can advise whether it suits you, particularly if you take other medications.
• For jet lag westward: usually doesn’t need melatonin — westward shifts align with the natural drift of human circadian rhythms.

What melatonin doesn’t do

• It’s not a sedative. If you’re anxious or your sleep environment is suboptimal, melatonin doesn’t make those issues go away.
• It doesn’t maintain sleep. Melatonin helps onset but doesn’t prevent middle-of-night awakening — that’s a different mechanism (cortisol regulation, autonomic balance, sleep environment).
• It doesn’t replace sleep hygiene. Heavy late-evening eating, alcohol, blue-light exposure, and irregular schedules disrupt sleep more than melatonin can fix.
• It’s not an antidote to caffeine. Caffeine and melatonin work through different receptors; the caffeine effect on sleep remains regardless of melatonin dose.

When CBT-I beats melatonin

For chronic insomnia (persistent sleep problems lasting weeks/months), cognitive-behavioural therapy for insomnia has a much stronger evidence base than melatonin, and its benefits tend to persist after treatment ends. CBT-I addresses the cognitive and behavioural patterns that maintain insomnia (clock-watching, in-bed wakefulness, anticipatory anxiety about sleep). It’s the recommended first-line treatment for chronic insomnia in clinical guidelines, so if sleep problems have lasted more than a few weeks, talk to your family doctor rather than relying on a supplement.

Practical takeaways

• Melatonin is a circadian timing signal, not a sedative. Effective for circadian problems (jet lag, shift work, phase delay) but produces small effects on garden-variety insomnia.
• More isn’t better. In the key dose trial, 0.3mg matched 3mg for sleep, and 3mg lingered into the next day. Most products contain 3-10mg; ask a pharmacist or clinician before choosing one.
• Timing matters as much as dose. For delayed sleep phase or shift work, get timing advice from a clinician, because mistimed melatonin can shift your clock the wrong way.
• Doesn’t maintain sleep, doesn’t replace sleep hygiene, doesn’t counter caffeine.
• For chronic insomnia: CBT-I has stronger and more durable evidence than melatonin — ask your family doctor about it.
• Check first if you’re pregnant, breastfeeding or taking other medications: Health Canada-authorised melatonin labels advise against use during pregnancy or breastfeeding, and a pharmacist can check for interactions.

References