Melatonin

What the evidence actually shows

Melatonin is one of the few supplements where the strongest research applications are not the ones it's most marketed for. The clearest current evidence supports use in shift-work and jet lag, sleep-onset insomnia (helping people fall asleep faster — not stay asleep), dysmenorrhea (period pain), reduction in exercise-related muscle damage in trained athletes, and improvements in quality of life in cancer patients undergoing treatment.

The evidence is good (but not definitive) for modest reductions in blood pressure, improvements in glycaemic markers, and reduced anxiety and depression scores in people with established sleep disturbance. It is generally weaker for "general sleep quality" in adults who do not have a circadian-rhythm or sleep-onset problem.

What melatonin does poorly is induce deep, restorative sleep on demand. It is a chronobiotic — a signal to the brain that it is biologically night — not a sedative. Used as a sleep aid in people whose sleep is disrupted by stress, screens, or alcohol, the effect is modest. Used to shift the body clock (jet lag, shift work, delayed sleep phase syndrome), the effect is reliably useful.

How it works

Melatonin is produced by the pineal gland in response to darkness, peaking 2–4 hours before usual sleep onset and falling rapidly at dawn. Its primary role is to signal biological night to the body — it does not put you to sleep, it tells your brain that conditions for sleep are now appropriate.

The synthetic form used in supplements is chemically identical to endogenous melatonin. Once ingested, it reaches peak blood levels within 30–60 minutes and clears within 4–8 hours, depending on dose and formulation.

The mechanism explains both its strengths and limitations. Taken in the evening, it advances the body clock and shortens sleep onset. Taken in the morning (as for night shift workers), it delays the clock. Taken at any time when the natural circadian signal is already correct, it adds little because the brain is already receiving the same message.

Who benefits most — and who should be cautious

The clearest beneficiaries are frequent travellers crossing 3+ time zones, shift workers, people with delayed sleep phase syndrome (chronic late bedtimes despite normal hours kept), older adults (whose natural melatonin production declines), and children with neurodevelopmental conditions under medical guidance.

It is less reliably useful for the much larger group of adults who simply struggle to fall asleep due to stress, late-night screen use, alcohol, or irregular schedules. In these cases, melatonin produces a modest effect — often less than addressing the underlying behaviour would.

The main caution is dose. Most products are dramatically overdosed compared to what trials show is effective. Pharmacological doses (3–10 mg) produce blood levels 10–100 times higher than the natural overnight peak, and the body's response to such high doses is unpredictable — sometimes producing daytime grogginess, vivid dreams, or paradoxical insomnia the following night.

People taking blood thinners, anticonvulsants, or immunosuppressants should consult a prescriber. Melatonin is generally not recommended in pregnancy due to limited safety data.

How to take it

Form. Immediate-release for sleep onset; extended-release for staying asleep or for older adults whose own production has declined.

Dose. Lower than most products provide:

• Sleep onset: 0.3–1 mg is the dose used in the strongest trials. Higher doses are not more effective and often less so.
• Jet lag: 0.5–3 mg taken at the destination bedtime for several nights
• Shift work: 1–3 mg before the desired sleep period

Timing. 30–60 minutes before intended sleep. For jet lag, 1–2 hours before bedtime in the new time zone, starting the day of travel.

Pair with darkness. Melatonin works with low light, not against bright light. Bright screens, lamps, or daylight exposure after taking it can blunt the effect.

Common misconceptions

Melatonin is a sleeping pill. It is not. It signals biological night but does not sedate. People expecting a pharmaceutical sleep effect are usually disappointed.

Higher doses work better. They do not. Trials consistently show that 0.3–1 mg produces equal or better effects than 5–10 mg, with fewer side effects.

It's risky to take long-term. Available evidence does not support significant long-term harm at standard doses. The main concern with daily use is masking an underlying sleep problem rather than addressing it.

It works for all sleep problems. It does not. Melatonin is most effective for circadian-rhythm issues (jet lag, shift work, delayed sleep phase) and for difficulty falling asleep. It does not reliably help with middle-of-the-night waking, sleep maintenance, or sleep disrupted by anxiety, pain, or sleep apnoea.

It causes dependence. Unlike GABAergic sleep aids (zolpidem, benzodiazepines), melatonin does not produce physical dependence. Tolerance to its effects can develop with very high doses but is uncommon at low doses.

FAQ

How long until it works? 30–60 minutes for sleep onset. For jet lag, several consecutive nights at the new bedtime.

Should I take it every night? For most healthy adults, no — use it for specific situations (travel, shift work, occasional sleep onset difficulty). Older adults with confirmed low natural production may benefit from nightly use.

Will it leave me groggy? At low doses (0.3–1 mg) most people have no morning hangover. At higher doses, daytime grogginess and vivid dreams are common.

Does it interact with medications? With anticoagulants, immunosuppressants, blood pressure medications, and some antidepressants. Mention regular melatonin use to your prescriber.

Can I give it to my children? Only under medical guidance. Routine use in healthy children is generally not recommended.

Evidence grades and benefit rankings on this page are sourced from Examine.com, an independent research database with no industry funding.