Melatonin

Melatonin is one of the most widely used sleep supplements in the world, with a substantial base of randomized controlled trial evidence. Its effects are most pronounced for circadian rhythm disruption , jet lag, shift work, and delayed sleep phase syndrome , and more modest for primary insomnia in otherwise healthy adults.

How It Works

Melatonin is a hormone produced by the pineal gland in response to darkness. As ambient light fades in the evening, the brain’s suprachiasmatic nucleus (the master circadian clock) signals the pineal gland to begin melatonin secretion. This rise in melatonin , called dim-light melatonin onset , tells the body that night has arrived and prepares it for sleep by lowering core body temperature and promoting drowsiness.

Supplemental melatonin mimics this endogenous signal. At low doses it acts as a chronobiotic (a substance that shifts the timing of the clock) rather than a sedative. At moderate-to-higher doses it also has mild hypnotic properties that can shorten the time needed to fall asleep.

Sleep Onset {#sleep-onset}

Meta-analyses of randomized controlled trials consistently show that melatonin reduces sleep onset latency , the time it takes to fall asleep , by roughly 7–18 minutes compared to placebo. A dose-response meta-analysis by Cruz-Sanabria et al. (2024, Journal of Pineal Research) found that the effect on sleep quality plateaus around 4 mg/day, with diminishing returns above that threshold. Timing relative to desired sleep onset matters: taking melatonin 30–60 minutes before bed is the standard approach for sleep onset support.

Melatonin does not meaningfully increase total sleep time in healthy adults who do not have circadian disruption. It is not a sedative in the classical sense and does not produce the same depth of pharmacological sleep as benzodiazepines or z-drugs. For chronic primary insomnia, cognitive behavioral therapy for insomnia (CBT-I) remains the first-line evidence-based treatment.

Circadian Rhythm {#circadian-rhythm}

Melatonin’s strongest and most consistent application is circadian phase shifting. For jet lag, a dose of 0.5–5 mg taken at the target destination’s local bedtime on the night of travel and for several days afterward can accelerate clock resynchronization and reduce daytime fatigue. For shift workers transitioning to daytime sleep, melatonin taken immediately before the intended sleep period can help improve sleep quality.

For delayed sleep phase syndrome , a condition where the internal clock is persistently set several hours too late , low-dose melatonin (0.5–1 mg) taken 5–7 hours before the desired sleep onset is more effective than higher doses for advancing the circadian phase. The chronobiotic effect is dose-sensitive: doses above 1 mg can saturate melatonin receptors and produce diminishing or unpredictable phase-shifting effects.

Cognitive Aging {#cognitive-aging}

A 2025 meta-analysis (PMC12581400) found that melatonin supplementation improved cognitive function markers in adults with mild cognitive impairment. The proposed mechanism involves melatonin’s antioxidant properties, its role in regulating mitochondrial function, and its potential to reduce amyloid pathology , all areas of active investigation. This application is most relevant for older adults rather than healthy younger populations.

Dosing

Goal	Dose	Timing
Sleep onset support	0.5–5 mg	30–60 min before bed
Jet lag / shift work	0.5–5 mg	At destination bedtime
Circadian phase advance	0.5–1 mg	5–7 hours before desired sleep

Starting at the lowest effective dose (0.5–1 mg) is generally recommended before escalating. Many commercial preparations contain 5–10 mg per dose, which exceeds what most evidence supports as optimal for phase shifting.

Safety

Melatonin has an excellent safety profile. It does not produce physical dependence, and rebound insomnia upon discontinuation has not been established in controlled research. Short-term adverse effects , mild headache, daytime drowsiness, dizziness , are self-limited and uncommon at standard doses. Long-term safety data in healthy adults beyond several months of continuous use is limited, though no concerning signals have emerged. It is not recommended during pregnancy or in children without medical supervision.