0.5–5 mg, 30–60 minutes before going to bed. Less is usually enough, especially in older adults. For jet lag, at the destination's bedtime.
Shortens the time to fall asleep and slightly improves quality and duration; a real but modest effect.
View the study (meta-analysis) →Effective for preventing and reducing jet lag when crossing several time zones.
See the study (Cochrane) →In older adults, low doses (0.5-2 mg) are usually enough; more is not better.
View the study (review) →*⏱ 3 min read
Melatonin is not just the sleep hormone: it regulates more than 500 genes and plays a key role in the body's antioxidant defenses, and as we age its production declines drastically: at age 50 levels are half of what they were at 20, and at age 80 production can be ten times lower than in adolescence, which has implications not only for sleep but for brain, cardiovascular, and immune health.
Melatonin follows a rhythm of approximately 24 hours synchronized with the light-dark cycle: levels begin to rise in the evening, peak around midnight, and fall to undetectable levels during the day; when it binds to the MT1 and MT2 receptors in the brain, it synchronizes the body's internal clock, lowers core body temperature, decreases the activity of wake-promoting neurons, and enhances the release of inhibitory neurotransmitters such as GABA, promoting conditions conducive to sleep without forcing it directly.
Several meta-analyses have investigated the effects of melatonin supplementation in adults with various sleep-related conditions, and in general it improves sleep duration, quality, and sleep-onset latency, although these effects are modest: in healthy adults without underlying conditions, melatonin increases total sleep time by 14-20 minutes and improves sleep-onset latency by 4-9 minutes; the effects are more pronounced in children and adolescents with neurodevelopmental disorders, where sleep latency improves by 20-25 minutes and total time by 25-41 minutes.
The most effective dose for reducing sleep-onset latency and increasing total sleep time ranges from 2 to 4 mg, with 3 mg appearing to provide the greatest benefit, significantly exceeding the usual dose of 2 mg; melatonin is most effective when taken 1 to 3 hours before bedtime or the desired sleep time, with administration 2-3 hours before maximizing the sleep-promoting effects by reducing onset latency by about 20 minutes; taken closer to bedtime, it is less effective.
The most interesting thing about melatonin is not its effect on sleep but its possible neuroprotective role: studies have observed lower melatonin levels in the cerebrospinal fluid of people with Alzheimer's disease, and higher risks of Alzheimer's in night-shift workers with disrupted melatonin production; melatonin reduces the production and improves the clearance of beta-amyloid plaques by blocking the enzymes that produce them and increasing their uptake into the brain's interstitial fluid for clearance via the lymphatic system.
Melatonin also blocks tau hyperphosphorylation, the process that leads to the formation of harmful neurofibrillary tangles; as a brain antioxidant, it can cross the blood-brain barrier and directly access neurons and mitochondria, where it neutralizes reactive oxygen and nitrogen species; and two meta-analyses suggest that melatonin administration improves cognitive function in adults with mild Alzheimer's, with stronger effects at low doses and medium-duration supplementation, even outperforming several pharmacological drugs such as donepezil on some parameters.
People over 50 should consider a small dose of melatonin (around 0.3 mg per night) to compensate for the age-related decline, given the hormone's excellent safety profile; studies show that doses of up to 50 mg daily do not reduce natural endogenous production, and unlike most pharmacological sleeping pills, melatonin does not create dependence or tolerance, which makes it a viable long-term tool for maintaining circadian rhythms and potentially protecting cognitive health.
Information, not medical advice. Scientific evidence reflects the quality of the studies.