Melatonin is the most widely used sleep supplement in the world — and one of the most widely misused. In many countries, melatonin is available over the counter as a sleep aid, marketed as a natural remedy for insomnia and sleep difficulty. The research on melatonin is more nuanced than this marketing suggests: it is effective for specific, well-defined sleep problems and largely ineffective for others, and the doses most people take are significantly higher than those supported by the evidence.
What Melatonin Actually Does
Melatonin is not a sedative. It does not induce sleep in the way that sleeping pills or alcohol do. It is a chronobiotic — a substance that influences the timing of the circadian clock. Its primary physiological role is signalling to the brain and body that darkness has arrived, initiating the cascade of physiological changes (core temperature reduction, heart rate slowing, cognitive quieting) that prepare the body for sleep.
Endogenous melatonin (produced naturally by the pineal gland) rises approximately 2 hours before habitual sleep time, peaks in the middle of the night, and declines toward waking. In a person with a well-functioning circadian rhythm and appropriate light exposure patterns, this melatonin rhythm naturally facilitates sleep onset and sleep maintenance.
When Melatonin Actually Works
Given melatonin’s chronobiotic rather than sedative mechanism, it is most effective for sleep problems that involve circadian timing disruption rather than sleep initiation difficulty per se.
Jet lag: The most evidence-supported use for melatonin. Taking melatonin at the target bedtime of the destination timezone (beginning on the day of travel for eastward travel, on arrival for westward travel) accelerates the resynchronisation of the circadian clock to the new timezone, reducing jet lag duration and severity. The evidence for this application is robust across multiple randomised controlled trials.
Delayed Sleep Phase Syndrome: A circadian rhythm disorder characterised by a naturally late sleep timing (night owls at an extreme) that conflicts with social and work schedules. Low-dose melatonin taken 5–6 hours before habitual sleep time can advance the circadian phase, shifting sleep timing earlier over several weeks. This is a medical application that benefits from professional guidance.
Shift work sleep adjustment: Melatonin can facilitate sleep during daytime hours for shift workers by providing the darkness signal at an unusual time of day. Effectiveness varies with individual response and requires timing guidance specific to the shift pattern.
When Melatonin Doesn’t Work — And Why People Take Too Much
For ordinary insomnia — difficulty falling or staying asleep in someone with a normal circadian rhythm — melatonin’s evidence base is weak. Multiple meta-analyses show small to modest effects on sleep onset latency (typically reducing it by 7–12 minutes) and sleep quality compared to placebo, with considerable variability across individuals. CBT-I, sleep hygiene improvements, and circadian optimisation produce larger, more durable effects on ordinary insomnia.
The dose issue: most over-the-counter melatonin products in the US contain 5–10mg of melatonin — doses 20–50 times higher than the endogenous peak of approximately 0.1–0.3mg. Research by Kennaway and Clarke at the University of Adelaide shows that optimal melatonin dosing for sleep is 0.5mg, taken 30 minutes before target sleep time. Higher doses produce supraphysiological blood levels that can actually disrupt sleep architecture and may suppress endogenous production over time with regular use.
The Practical Guidance
For jet lag: melatonin at 0.5–1mg taken at the destination bedtime is well-supported. For ordinary difficulty sleeping: prioritise circadian optimisation (morning light, consistent timing, evening light reduction) and sleep hygiene improvements — these address the underlying mechanisms more effectively than melatonin. If using melatonin, start with the lowest available dose (0.5mg) rather than the marketing-prominent high doses. Do not use melatonin for longer than 2–4 weeks without medical guidance.
This content is for informational purposes only and is not a substitute for professional medical advice. Consult a healthcare professional before using melatonin if you are pregnant, taking medications, or have existing health conditions.