Melatonin

What Melatonin Is

Melatonin is the hormone the pineal gland secretes when the master clock in the suprachiasmatic nucleus decides it is night. In a person living under natural light, blood levels begin to rise a couple of hours before habitual sleep, peak in the middle of the night and fall to nothing by morning. That rise — the dim-light melatonin onset, or DLMO — is the most reliable marker of circadian phase that can be measured in a human being, because it is masked by bright light and almost nothing else.

Swallowed as a tablet, melatonin does two separable things. At bedtime it is a mild sleep-promoting signal. Taken earlier, in the afternoon or early evening, it moves the clock. Most of the confusion about whether melatonin "works" comes from testing it for the first job when its real strength is the second. The dosing argument is covered in depth in Melatonin: Optimal Dosing and the Low-Dose Debate.

What the Evidence Actually Shows

Delayed sleep phase — the strongest indication. A meta-analysis of nine placebo-controlled trials in delayed sleep phase disorder found that melatonin advanced the melatonin onset by 1.18 hours, moved sleep-onset time 0.67 hours earlier and cut sleep latency by 23 minutes. A 2018 trial of 116 adults with delayed sleep-wake phase disorder gave 0.5 mg one hour before desired bedtime alongside behavioural scheduling: sleep began 34 minutes earlier than on placebo, and 53% were rated improved versus 24%. The American Academy of Sleep Medicine's circadian guideline endorses strategically timed melatonin for this disorder.

Jet lag. A Cochrane review of ten trials found that melatonin taken at destination bedtime reduced jet lag after five or more time zones in nine of them, with a number needed to treat of two. Doses from 0.5 to 5 mg worked; 5 mg brought faster sleep onset than 0.5 mg; more than 5 mg added nothing, and a 2 mg slow-release form was relatively ineffective.

Insomnia — modest at best. A meta-analysis of 19 randomised trials in 1,683 people found melatonin shortened sleep onset by 7 minutes and lengthened total sleep by 8 minutes. The same AASM that endorses it for circadian disorders suggests against it for chronic insomnia in adults. One earlier meta-analysis separated the two uses cleanly: 39 minutes faster sleep onset in delayed phase, 7 minutes in insomnia.

Older adults. Three trials of prolonged-release 2 mg in people over 55 showed small but consistent gains in sleep quality and morning alertness over three weeks, with no rebound insomnia and no tolerance over six months.

The Dose Question

The landmark dose-ranging study gave insomniacs over 50 a week each of 0.1, 0.3 and 3 mg. The 0.3 mg dose restored sleep efficiency and brought plasma melatonin back into the normal nocturnal range. The 3 mg dose also improved sleep — but caused measurable hypothermia and left plasma melatonin elevated into the daylight hours. Healthy young adults given 0.3 mg reached normal night-time blood levels and fell asleep faster with no morning hangover.

Two findings complicate the clean story. A 2013 meta-regression found that higher doses and longer trials produced larger effects on sleep onset and total sleep. And in jet lag, 5 mg outperformed 0.5 mg for falling asleep. The honest reading is a trade-off: low doses reproduce physiology with fewer side effects; higher doses are a stronger hypnotic with a longer tail. For shifting the clock, 0.5 mg timed correctly does the job.

What You Are Actually Buying

A laboratory analysis of 31 commercial melatonin products found actual content ranging from 83% below to 478% above the label, with lot-to-lot variation up to 465%. Over 71% were not within 10% of their stated dose, and a quarter contained serotonin. In the United States melatonin is a supplement; in most of the European Union it is a prescription medicine. If precision matters — and for a 0.3 mg physiological dose it does — buy a pharmaceutical-grade or independently tested product.

Safety

Across 37 placebo-controlled trials at doses up to 12 mg, the commonest adverse effects were daytime sleepiness (1.7%), headache, dizziness and hypothermia (each under 1%), with no life-threatening events. High-dose trials (10 mg and above) show no excess of serious adverse events but a 40% higher rate of drowsiness, headache and dizziness. Long-term randomised data beyond a few months barely exist.

Children are a separate concern. US poison-centre reports of paediatric melatonin ingestion rose more than fivefold in a decade, mostly unintentional ingestions by children under five, with five needing ventilation and two deaths. Keep gummies out of reach, and do not give melatonin to a child without a clinician's plan.

Where It Fits

Melatonin is the pharmacological layer of the Circadian Optimization Protocol, where it sits behind the three anchors that move the clock without a tablet: morning light, a fixed wake time and an early, consistent meal window. If your problem is sleep depth rather than timing, the Deep Sleep Stack addresses different mechanisms and is compatible with low-dose melatonin.

Related Research

• Melatonin: Optimal Dosing and the Low-Dose Debate
• Circadian Light: Managing Blue Light and Morning Sun
• The Circadian Optimization Protocol: Light + Melatonin + Timing
• The Circadian Optimization Protocol
• Magnesium L-Threonate