Melatonin: Benefits, Risks, and Safe Use

Intro

Melatonin is the most widely used sleep supplement in the world. In many countries it is available over the counter; in others it is prescription-only. Consumer interest has grown dramatically, but the evidence base is often misunderstood: melatonin is not a sleeping pill. It is a circadian signal.

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Key Points

Melatonin is a hormone — a signal to the body that night has arrived. It shifts the timing of sleep rather than sedating.
It is most effective for jet lag, shift work, and delayed sleep phase syndrome.
Evidence for treating chronic insomnia is weak. CBT-I is far more effective.
Effective doses are 0.5–1 mg. Most commercial products are substantially overdosed at 5–10 mg.
Timing matters more than dose — take melatonin 1–2 hours before the desired sleep time.
Non-habit-forming and generally safe short term. Long-term safety data, particularly in children, are limited.

What Melatonin Is

Melatonin (N-acetyl-5-methoxytryptamine) is a hormone produced by the pineal gland, primarily at night in response to darkness. Secretion begins 1–3 hours before habitual sleep time, peaks during the middle of the night, and declines before dawn. It acts as a timing signal to the circadian clock — telling the body that it is night and that sleep is appropriate — but it does not cause sleep directly.

Exogenous melatonin (supplemental or prescription) mimics this signal. Its primary pharmacological effect is to shift the phase of the circadian clock — either advancing it (moving sleep earlier) or delaying it (moving sleep later), depending on when it is taken.

This makes melatonin a chronobiotic (circadian clock-shifter), not a traditional hypnotic.

What the Evidence Shows

Jet lag

Melatonin has the strongest evidence base for jet lag. Crossing multiple time zones misaligns the circadian clock with the local environment. Taking melatonin at the destination’s local bedtime accelerates clock re-entrainment and reduces jet lag symptoms — broken sleep, daytime drowsiness, and impaired concentration.

Practical use: Take 0.5–1 mg at the local bedtime of your destination, starting on the day of travel, for 2–4 days. Eastward travel (which requires phase advance) benefits most.

Shift work sleep disorder

People working night shifts, early mornings, or rotating schedules frequently develop shift work sleep disorder — difficulty sleeping at the required time and excessive sleepiness when awake. Taking melatonin at the intended sleep time (e.g. on returning home after a night shift) can shorten sleep onset and improve daytime sleep duration.

Melatonin is most effective as part of a broader strategy that includes light therapy to block alerting light signals at the right time, and sleep hygiene practices adapted to the shift schedule.

Delayed sleep phase syndrome

Delayed sleep phase syndrome (DSPS) is a circadian rhythm disorder in which the sleep-wake cycle is chronically shifted several hours later than conventional timing — people cannot fall asleep until 2–4 am or later and struggle to wake before midday. It is more common in adolescents and young adults.

Low-dose melatonin (0.5 mg) taken 5–6 hours before the habitual sleep onset time gradually shifts the clock earlier over several weeks. This is the phase-advance window; melatonin taken at other times has different and sometimes counterproductive effects.

Insomnia

Evidence for melatonin in treating chronic insomnia is modest. Meta-analyses find that melatonin reduces sleep onset latency by approximately 7 minutes and slightly improves total sleep time — effects unlikely to be clinically meaningful for people with significant insomnia.

Melatonin does not address the perpetuating behavioural and cognitive factors that maintain chronic insomnia. CBT-I remains the first-line treatment.

Exception: Prolonged-release melatonin (2 mg) has some evidence for improving sleep quality in adults aged 55 and over, in whom melatonin secretion naturally declines with age. This is a licensed indication in some countries.

Other uses

Pre-operative anxiety: Used in some paediatric anaesthetic protocols to reduce anxiety before procedures
ICU patients: Some evidence for reducing delirium in hospitalised patients; research ongoing
Children with neurodevelopmental conditions: Used under clinician supervision for sleep initiation in children with ADHD and autism spectrum disorder, where the evidence base is moderate

Dosing

The over-dosing problem

Most commercial melatonin products contain 5–10 mg per dose. Physiologically active doses in controlled human studies are 0.1–1 mg. The supraphysiological amounts in most products may cause next-morning grogginess, suppress the body’s own melatonin production with chronic use, and produce non-linear or counterproductive effects at certain times of day.

Recommended dose: 0.5–1 mg is as effective as higher doses for most uses. Start with the lowest available dose.

Timing

Timing is the critical variable — often more important than dose:

Use	When to take
Jet lag (eastward travel)	Local bedtime at destination, starting day of travel
Jet lag (westward travel)	Local bedtime at destination or shortly before
Shift work (night shift)	Morning after night shift, at the start of intended sleep
Delayed sleep phase	5–6 hours before current habitual sleep time; shift earlier gradually
General sleep onset aid	1–2 hours before intended sleep time

Side Effects

Melatonin is generally well-tolerated. Reported side effects are mild and include:

Next-morning grogginess or “hangover” (most common at higher doses)
Headache
Dizziness
Nausea
Vivid dreams or nightmares

Melatonin does not cause physical dependence or rebound insomnia on stopping.

Safety Considerations

Short-term use (days to weeks): Well-established safety profile in adults.

Long-term use: Limited long-term data in adults. If using nightly for months without a clear circadian indication, consider whether CBT-I or treatment of an underlying condition is more appropriate.

Children: Should not be given without medical supervision. Long-term effects on pubertal development have not been ruled out.

Pregnancy and breastfeeding: Insufficient safety data; avoid unless directed by a clinician.

Drug interactions:

Warfarin and anticoagulants — melatonin may enhance anticoagulant effect; monitoring required
CNS depressants — additive sedative effect
Immunosuppressants — theoretical interaction; discuss with prescriber

Regulatory status: Melatonin is a prescription-only medicine in the UK, Australia, and several European countries. It is available over the counter in the US, Canada, and many other countries. OTC product quality and actual melatonin content vary widely between brands where unregulated.

What Melatonin Cannot Do

Treat chronic insomnia effectively — CBT-I does this
Compensate for chronically insufficient sleep
Fix the underlying causes of poor sleep — sleep hygiene and treatment of contributing conditions are needed
Replace clinical evaluation when the cause of poor sleep is unknown

FAQ

Q: What does melatonin actually do?
A: It signals to the body that night has arrived, shifting the timing of the sleep-wake cycle. It adjusts circadian timing rather than sedating — most effective for jet lag, shift work, and delayed sleep phase.

Q: What is the right dose?
A: 0.5–1 mg is as effective as higher doses. Most OTC products are substantially overdosed. Timing matters more than dose — take 1–2 hours before the desired sleep time.

Q: Is melatonin safe?
A: Generally safe for short-term use in adults. Non-habit-forming. Long-term data are limited; not recommended for children without medical guidance.

Q: Can it treat chronic insomnia?
A: Evidence is weak. CBT-I is far more effective. Melatonin can support circadian-related sleep difficulty but does not address the perpetuating cycle of chronic insomnia.

Q: Is there a best time to take melatonin?
A: Yes — timing is critical. For jet lag, take it at the local bedtime of your destination. For shift work, at the start of your intended sleep window. For general use, 1–2 hours before intended sleep. For delayed sleep phase, 5–6 hours before your current habitual sleep time.