Melatonin: Optimal Dosing, Timing and When to Avoid It

A Timing Signal, Not a Sedative

Endogenous melatonin rises about two hours before habitual sleep onset, peaks in the middle of the biological night, and falls before waking. It does not cause sleep; it signals that the biological night has begun, and the sleep system responds to that signal in combination with accumulated sleep pressure.

This distinction has direct practical consequences. Taking melatonin at bedtime provides a signal the body has already generated, which is why the effect on sleep onset is small. Taking it several hours before habitual sleep onset shifts the clock earlier, which is why phase-shifting works.

The tool for understanding this is the phase response curve. Melatonin taken in the hours before the endogenous rise advances the clock, making sleep and waking occur earlier. Taken in the second half of the night or early morning, it delays the clock. The size of the shift depends on timing far more than on dose.

What the Evidence Supports

Jet lag

The strongest indication. Meta-analyses support melatonin for reducing jet lag symptoms, particularly for eastward travel across several time zones, taken at the target destination bedtime. Effects are clinically meaningful.

Delayed sleep phase

Well supported. In people whose clock runs late, melatonin taken several hours before desired sleep time advances the phase, and this is a recognised clinical use with dosing guidance emphasising small doses and correct timing.

Shift work

Modest support for improving daytime sleep duration after night shifts.

Primary insomnia

Meta-analyses find statistically significant but small effects: sleep onset latency reduced by roughly seven minutes and total sleep time increased by a similar order. Clinical guidance in several countries does not recommend melatonin as first-line for chronic insomnia, where cognitive behavioural therapy for insomnia has substantially better evidence.

Older adults

Endogenous melatonin declines with age, and prolonged-release melatonin is licensed in several jurisdictions for insomnia in adults over fifty-five, with modest efficacy.

Beyond sleep

Melatonin is an antioxidant and has been studied in oncology support, delirium prevention and metabolic contexts, generally at higher doses. These are clinical research areas rather than established uses.

Dose: Less Is More

The dose-response relationship for melatonin is not what the market implies.

Physiological replacement is achieved at roughly 0.3 milligrams, which produces plasma concentrations similar to the natural nocturnal peak. Studies comparing doses have found 0.3 milligrams as effective as 3 milligrams for sleep onset in older adults, with fewer residual effects, and phase-shifting work uses doses of 0.5 milligrams effectively.

Doses of 3, 5 and 10 milligrams produce plasma concentrations many times physiological, sustained well into the following day, which is the source of next-day grogginess and may desensitise receptors. Higher doses can also produce a phase shift in the unintended direction if the timing is wrong, because the elevated concentration persists into a different part of the phase response curve.

Practical dosing:

• Sleep onset difficulty: 0.3 to 1 mg, thirty to sixty minutes before bed.
• Phase advance for a late clock: 0.5 mg, four to six hours before current sleep onset, alongside morning light exposure.
• Eastward jet lag: 0.5 to 3 mg at target bedtime for several nights, starting on arrival.
• Avoid: taking a large dose at 3am when unable to sleep, which delivers a delaying signal at the wrong point in the curve.

The Product Quality Problem

This deserves emphasis because it is unusually bad in this category.

Independent analyses of commercial melatonin products have found actual content varying substantially from the label, in both directions, with a meaningful proportion falling outside a reasonable tolerance and some products containing serotonin as a contaminant. Analyses of gummy products have found even greater variability, which is a specific concern given how frequently melatonin gummies are given to children.

Regulatory status varies: melatonin is a prescription medicine in the United Kingdom, the European Union and Australia, and a dietary supplement in the United States. The jurisdictions regulating it as a medicine apply pharmaceutical manufacturing standards, which is one argument for prescription products where available.

Reported paediatric melatonin ingestions have risen sharply in several countries, which reflects both increased use and the accessibility of sweet-tasting products.

Safety and When to Avoid It

Melatonin is well tolerated short term, with headache, next-day grogginess, vivid dreams and nausea the common reports.

Considerations. Long-term safety in adults is not well characterised, since most trials are short. In children and adolescents, effects on pubertal timing are theoretically plausible given melatonin's role in reproductive signalling in some species, and human evidence is reassuring but limited; paediatric use belongs with a clinician. Melatonin has immunomodulatory activity, which is a consideration alongside immunosuppressive therapy. It may affect glucose handling in the morning, and it interacts with fluvoxamine, which substantially raises melatonin concentrations by inhibiting its metabolism. Anticoagulant interaction has been reported.

When not to reach for it. Melatonin is the wrong tool for waking during the night, for unrefreshing sleep despite adequate duration, which may indicate sleep-disordered breathing, and for chronic insomnia where cognitive behavioural therapy is the evidence-based option. Using it nightly for years without addressing why sleep is poor is the most common misuse.