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Mel8.5
Melatonin Research
Likely helps
1,028 peer-reviewed studies
What the evidence says
Likely helps
Melatonin appears to help in 19 of 24 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 2002–2026 with a typical study size of 227 participants.
Based on 1,028 studies · 206 meta-analyses · 684 RCTs · 32,164 total participants
Confidence
High confidence
What the studies found
19helped4unclear1didn't help· 1004 more without graded effect data
By outcome
Sleep & insomniaReduces sleep latency by 7-12 minutes · 30-60 minutes · Modest improvement with extended-release forms · 1 week · Modest improvement in slow-wave sleep architecture · 1-2 weeks
Fertility & reproductiveMay support reproductive health and fertility markers · 4-12 weeks
Mostly mechanism / observational10 studies
Weight management
Mostly mechanism / observational5 studies
Inflammation
Mostly mechanism / observational3 studies
Men's vitality
Mostly mechanism / observational3 studies
By the numbers
Pulled from 56 studies with measurable effects
Likely real effects
87%
across studies
People studied
32k
typical study: 227 people
Strongest designs
890
206 pooled, 684 randomised
Showed benefit
79%
19/24 studies
How long studies ran
1–3 months
1
3+ months
3
Populations Studied
Adults with sleep disorders2
Patients with dementia2
General population2
PCOS patients2
Active research area
459 studies in the last 5 years · Latest meta-analysis: 2026
200220142026
1Cognitive function in mild cognitive impairment and Alzheimer'sMeta-AnalysisCited 18×n=4,599 · very large study2024
Melatonin may be a better potential disease-modifying treatment for cognitive decline in mild AD and MCI.
Terao I et al. · Journal of Alzheimer's disease : JAD (2024)
Melatonin may be a better potential disease-modifying treatment for cognitive decline in mild AD and MCI.
Aerobic exercise for a short time might also be better than donanemab, lecanemab and aducanumab if continued, as it is well tolerated and more effective, although less valid due to heterogeneity.
Another limitation is the small number of participants.
2Insomnia symptomsMeta-AnalysisCited 17×n=4,875 · very large study2023
PR melatonin for individuals with a mean age ≥ 55 and ramelteon show larger effect sizes.
Maruani J et al. · Journal of sleep research (2023)
For the subgroup mean age of patients ≥55, PR melatonin was efficacious on oSE with a large effect size (p < 0.001; weighted difference = 2.95%).
Regarding long-term effects, ramelteon has a large effect size on oTST (p < 0.001; weighted difference = 2.02 min) and sTST (p < 0.001; weighted difference = 14.5 min).
PR melatonin and ramelteon appear efficacious compared with placebo for insomnia symptoms with PR melatonin showing mostly small to medium effect sizes.
3Delirium prevention and mortality reductionMeta-AnalysisCited 7×n=4,850 · very large study2023
This study provides evidence of the potential effects of MRAs in preventing delirium and reducing mortality.
Wada M et al. · General hospital psychiatry (2023)
Barely noticeable benefit
← WorseNo effectBetter →
Likely real
Additionally, MRAs were associated with a significant reduction in mortality rate (risk ratio = 0.90, p = 0.02) in delirium prevention studies.
This study provides evidence of the potential effects of MRAs in preventing delirium and reducing mortality.
Further research is required to elucidate the therapeutic potential of MRAs for delirium and identify specific patient populations that may benefit from this agent.
5Sleep onset latency and total sleep timeMeta-AnalysisCited 31×n=1,998 · large study2022
We found evidence that melatonin significantly improved sleep onset latency and total sleep time, but not sleep awaking, in children and adolescents with a variety of neurodevelopmental disorders, and sleep onset latency (measured by diary) as well as total sleep time (measured with polysomnography) in adults with delayed sleep phase disorder.
Salanitro M et al. · Neuroscience & Biobehavioral Reviews (2022)
We found evidence that melatonin significantly improved sleep onset latency and total sleep time, but not sleep awaking, in children and adolescents with a variety of neurodevelopmental disorders.
No evidence of significant differences between melatonin and placebo was found in terms of tolerability.
7Manic symptoms in bipolar disorderMeta-AnalysisCited 22×n=1,279 · large study2022
There is a paucity of studies examining pharmacological interventions for sleep and circadian rhythm disturbance in BD.
McGowan NM et al. · CNS drugs (2022)
No clear effect
← WorseNo effectBetter →
The largest efficacy signal detected was for manic symptoms (four studies; g = - 0.44 [95% CI - 1.03 to 0.14]) but there was substantial heterogeneity between studies and patient characteristics.
There is a paucity of studies examining pharmacological interventions for sleep and circadian rhythm disturbance in BD.
Few studies assessed sleep-related symptoms, and none quantitatively examined endogenous melatonin patterns or other circadian rhythms.
9Fatigue incidence in cancer patientsMeta-AnalysisCited 3×n=126 · medium study2025
The available evidence is of very low certainty, so we are unable to draw conclusions about the effects of melatonin on quality of life and sleep at three months in people receiving treatment for cancer.
Yu ZY et al. · The Cochrane database of systematic reviews (2025)
Huge benefit
← WorseNo effectBetter →
We downgraded the certainty of the evidence because of high risk of bias, small sample size, the width of the 95% confidence interval, and indirectness due to inadequate reporting of cancer type.
Melatonin likely reduces the incidence of fatigue (RR 0.46, 95% CI 0.39 to 0.55; 10 studies, 1359 participants; moderate-certainty evidence) and may reduce nausea (RR 0.85, 95% CI 0.72 to 1.00; 6 studies, 710 participants; low-certainty evidence).
We downgraded the certainty of the evidence because of the high risk of bias and the width of the 95% confidence interval.