Benefits
Sleep onset latency — modest effect in adults
Ferracioli-Oda 2013 meta-analysis (PLOS One): melatonin reduces sleep onset latency by ~7 minutes and increases total sleep time by ~8 minutes vs placebo. Cruz-Sanabria 2024 (J Pineal Res 76:e12985, PMID 38888087) dose-response meta-analysis: effect peaks at 4 mg/day administered 3 hours before bedtime. Honest framing: effect smaller than benzodiazepines or Z-drugs, but with much better safety profile.
Children and adolescents — stronger evidence
Choi 2022 meta-analysis (Sleep Med Rev, PMID 36179487) of 24 RCTs found melatonin significantly improved sleep onset latency and total sleep time in children and adolescents with chronic insomnia, but NOT in adults with non-comorbid insomnia. Particularly effective in pediatric ASD, ADHD, and neurodevelopmental disorders where intrinsic melatonin signaling may be disrupted.
Jet lag — strongest indication
Cochrane review supports melatonin for jet lag, particularly when crossing 5+ time zones eastward. Standard protocol: 0.5–3 mg at destination bedtime starting day of arrival, continuing 2–5 days. Reduces jet lag severity (fatigue, daytime drowsiness, sleep disturbance) and accelerates circadian re-entrainment. One of the few sleep applications where melatonin's evidence is robust and consensus-supported.
Shift work sleep disorder
Modest evidence for daytime sleep improvement in night-shift workers when taken before daytime sleep periods. Effect is on subjective sleep quality and total daytime sleep duration. Doesn't fully resolve circadian misalignment — adjunct to bright-light therapy and proper sleep hygiene rather than standalone solution. AAFP guidelines include melatonin as reasonable option.
Eye health and AMD — observational only (caveat important)
Jeong 2024 (JAMA Ophthalmol 142:648-654, PMID 38842832) retrospective cohort of 121,523 adults aged 50+ in TriNetX EMR database: melatonin use associated with 58% lower AMD development risk and 56% lower nonexudative-to-exudative progression risk. Critical caveat: observational only, not an RCT. Hypothesis-generating, not causally established. Mechanism: melatonin is produced locally in retina, declines with age, has antioxidant + anti-VEGF activity.
Preoperative anxiety reduction
Multiple meta-analyses show melatonin (3-5 mg, 60-90 min preoperatively) reduces preoperative anxiety scores comparable to midazolam in some studies, with less postoperative grogginess. Reasonable option for surgical anxiety, particularly in older adults where benzodiazepine grogginess is undesirable. Effect on postoperative pain and opioid requirement also reported but less consistent.
Cancer-related fatigue and adjunctive oncology
Multiple RCTs in chemotherapy and radiotherapy patients show modest reductions in cancer-related fatigue with melatonin (typically 20-40 mg/day, much higher than sleep doses). Mechanism via antioxidant, anti-inflammatory, and circadian effects. Italian oncologist Paolo Lissoni's research program contributed much of this evidence — independent replication exists but is limited.
Migraine prevention — preliminary
Small RCTs report 3 mg melatonin nightly reduces migraine frequency comparable to amitriptyline 25 mg with fewer side effects. Evidence base smaller than for established preventives like topiramate or CGRP antagonists. Reasonable adjunct for those preferring melatonin's safety profile, but not first-line per current guidelines.
Most products contain wrong dose
Cohen 2017 analysis found 71% of US melatonin supplements deviated by ≥10% from label claim, with content ranging from -83% to +478%. Many retail tablets contain 5-10 mg — far above physiological doses. Recommendation: choose USP-verified products and start at 0.5-1 mg. Higher doses do not produce stronger sleep effects and may cause next-day grogginess.
Mechanism of action
Regulates Circadian Rhythm
Melatonin, a hormone produced by the pineal gland, binds to MT1 and MT2 receptors in the brain, signaling darkness to synchronize the body’s sleep-wake cycle with the day-night cycle.
Promotes Sleep Onset
By activating melatonin receptors in the suprachiasmatic nucleus (SCN), melatonin inhibits wake-promoting signals, reducing alertness and facilitating sleep initiation.
Antioxidant Activity
Melatonin neutralizes free radicals and upregulates antioxidant enzymes (e.g., superoxide dismutase), protecting cells from oxidative stress and damage.
Anti-Inflammatory Effects
Melatonin inhibits pro-inflammatory cytokines and modulates pathways like NF-kB, reducing inflammation in tissues such as the brain and immune system.
Modulates GABA and Serotonin Activity
Melatonin enhances GABA receptor activity, promoting calming effects, and may influence serotonin levels, contributing to mood regulation and sleep.
Neuroprotective Effects
By reducing oxidative stress and stabilizing neuronal membranes, melatonin protects brain cells, potentially supporting conditions like neurodegeneration or retinal health.
Regulates Autonomic Nervous System
Melatonin lowers sympathetic activity, reducing heart rate and blood pressure, which may contribute to its calming and antihypertensive effects.
Immune System Modulation
Melatonin influences immune cell function, enhancing T-cell activity and cytokine balance, potentially boosting immune responses.
Clinical trials
Systematic review and dose-response meta-analysis of 26 RCTs (1989-2020), 1,689 observations. Sleep onset latency reduction and total sleep time increase peak at 4 mg/day. Timing matters: 3 hours before desired bedtime more effective than 30 minutes before. Significantly more effective in insomnia patients than healthy volunteers. Practical: most users take it too late and at too high a dose.
Meta-analysis of 24 RCTs (20 non-comorbid + 4 comorbid insomnia, n=1,912). Children and adolescents: significant improvement in sleep onset latency and total sleep time. Adults: NOT significantly effective for sleep onset latency, total sleep time, or sleep efficiency in non-comorbid insomnia. Important honesty correction to common adult-use assumptions.
19 RCTs in 1,683 subjects with primary sleep disorders. Sleep latency reduced by ~7 min (WMD -7.06, 95% CI -9.75 to -4.37, p<0.001). Total sleep time increased by ~8 min (WMD 8.25, p=0.013). Sleep quality also improved (SMD 0.22). Effects persist with continued use. Modest absolute benefit but excellent safety profile.
Retrospective cohort study of 121,523 adults aged 50+ from TriNetX EMR database. Melatonin use associated with 58% reduction in AMD development risk (HR 0.42). Among 66,253 with nonexudative AMD: 56% reduction in progression to exudative AMD. Critical limitation: observational design cannot establish causation. Hypothesis-generating; warrants prospective RCT confirmation before clinical recommendation.
Strongest pediatric evidence base. Meta-analyses show 1-10 mg melatonin reduces sleep onset latency by 28-39 minutes and increases total sleep by 22-50 minutes in children with autism spectrum disorder. MENDS trial (Gringras 2012) and follow-up trials support 1-2 mg starting dose with titration. FDA-approved Slenyto® (pediatric prolonged-release formulation) supports formal pediatric sleep indication.