Melatonin

See our Evidence Standards for how we grade the research below.

What It Is

Melatonin (5-methoxy-N-acetyltryptamine) is an indoleamine hormone synthesized from tryptophan and released mainly by the pineal gland, almost entirely at night, under direct suppression by light exposure to the retina. It acts through two G protein-coupled receptors, MT1 and MT2, concentrated in the suprachiasmatic nucleus (SCN), the hypothalamic structure that functions as the body's master circadian clock, along with the retina, cardiovascular system, and immune tissue. Its primary physiological role is less to sedate directly and more to signal darkness, helping synchronize the timing of the body's internal rhythms, sleep among them, to the local day-night cycle. Endogenous production is highest in early childhood and declines substantially with age, which is part of why exogenous melatonin has been studied both as a circadian and sleep-timing agent and, more speculatively, as an intervention tied to the antioxidant and mitochondrial changes that accompany aging.

Melatonin's regulatory status is genuinely unusual among the hormones on this site. In the United States, oral melatonin is sold as an unregulated dietary supplement under DSHEA, not as an FDA-approved drug, which means no federal manufacturing standard guarantees that what's in the bottle matches the label. That's a real difference from thyroid hormone and DHEA, which are either prescribed or available as regulated, FDA-approved formulations. Prescription melatonin receptor agonists that act on the same MT1/MT2 receptors, ramelteon and tasimelteon in the US, and a slow-release melatonin product (Circadin) approved in Europe for adults 55 and older, are approved drugs with the manufacturing oversight that entails. Melatonin itself is not, a distinction worth understanding before treating any two melatonin products, or any two "melatonin" claims, as equivalent.

The Evidence — Mechanism and Age-Related Decline

Liu J, Clough SJ, Hutchinson AJ, Adamah-Biassi EB, Popovska-Gorevski M, Dubocovich ML. "MT1 and MT2 Melatonin Receptors: A Therapeutic Perspective." Annual Review of Pharmacology and Toxicology. 2016;56:361-383. PMID: 26514204. Pharmacology review describing how melatonin activates the MT1 and MT2 receptors to produce its effects on sleep and circadian timing, mood, learning and memory, and neuroprotection, and how synthetic ligands (ramelteon, tasimelteon, agomelatine, and slow-release melatonin) target these same receptors for approved clinical uses. The review also notes melatonin receptor signaling has been studied in cancer biology, the mechanistic thread picked up in the emerging-research section below.

Pharmacology review Endpoint: Receptor mechanism (MT1/MT2 signaling)

Touitou Y. "Human Aging and Melatonin. Clinical Relevance." Experimental Gerontology. 2001 Jul;36(7):1083-1100. PMID: 11404053. Review of melatonin's lifespan pattern: levels are highest in children younger than 4 years and decline progressively with age thereafter. As a chronobiotic, melatonin phase-shifts the sleep-wake cycle depending on when it's administered, with documented benefit in delayed and advanced sleep phase syndromes and in re-entraining travelers and shift workers. The review also notes melatonin's free-radical scavenging properties, observed mainly in vitro at pharmacological concentrations well above what typical supplementation achieves in the body.

Review Endpoint: Physiological pattern (age-related secretion decline)

The Evidence — Sleep and Circadian Use

Ferracioli-Oda E, Qawasmi A, Bloch MH. "Meta-Analysis: Melatonin for the Treatment of Primary Sleep Disorders." PLoS ONE. 2013 May 17;8(5):e63773. PMID: 23691095. Meta-analysis of 19 randomized, placebo-controlled trials, 1,683 subjects with primary sleep disorders. Melatonin significantly reduced sleep onset latency (weighted mean difference 7.06 minutes, 95% CI 4.37–9.75), increased total sleep time (WMD 8.25 minutes, 95% CI 1.74–14.75), and improved overall sleep quality (standardized mean difference 0.22, 95% CI 0.12–0.32). Trials using higher doses and longer duration showed larger effects on latency and total sleep time. The authors describe the effect as real but modest, and note it did not appear to diminish with continued use.

Meta-analysis of 19 RCTs (N=1,683) Endpoint: Clinical outcome (sleep latency, total sleep time, sleep quality)

Yue JL, Chang XW, Zheng JW, et al. "Efficacy and Tolerability of Pharmacological Treatments for Insomnia in Adults: A Systematic Review and Network Meta-Analysis." Sleep Medicine Reviews. 2023 Apr;68:101746. PMID: 36701954. Network meta-analysis of 69 trials, 17,319 patients, comparing 20 insomnia medications head-to-head, including melatonin receptor agonists (MRAs) as a drug class. Orexin receptor antagonists ranked best overall for sleep latency, time awake after sleep onset, and sleep efficiency, outperforming both Z-drugs and MRAs on those measures. MRAs showed efficacy specifically for sleep-onset insomnia with a favorable safety profile, but the review found the long-term adverse effects of every drug class studied, MRAs included, remain unclear.

This trial network is built around melatonin receptor agonists as a drug class, principally the prescription drug ramelteon, rather than OTC melatonin itself. Both act on the same MT1/MT2 receptors, so the comparative ranking is informative, but it is not a head-to-head trial of the specific melatonin supplement a patient buys off a shelf.

Network meta-analysis of 69 RCTs (N=17,319), 20 drug classes Endpoint: Clinical outcome (sleep latency, time awake after onset, sleep efficiency)

Herxheimer A, Petrie KJ. "Melatonin for the Prevention and Treatment of Jet Lag." Cochrane Database of Systematic Reviews. 2002;(2):CD001520. PMID: 12076414. Cochrane review of 9 usable randomized, placebo-controlled trials in air travelers, airline staff, and military personnel. Nine of ten trials found that melatonin taken near the target bedtime at the destination (10pm to midnight) reduced jet lag after flights crossing five or more time zones, with a calculated number needed to treat of 2. Doses between 0.5 and 5 mg were similarly effective, though people fell asleep faster and slept better at 5 mg than at 0.5 mg; doses above 5 mg showed no added benefit.

Timing mattered more than dose in this review. Melatonin taken at the wrong time, early in the day, was liable to cause sleepiness and delay adaptation rather than help it. The review's adverse-event search also surfaced case reports of harm in people with epilepsy and in patients taking warfarin, populations where melatonin use deserves a conversation with a physician rather than self-directed use.

Cochrane review of 9 RCTs Endpoint: Clinical outcome (jet lag severity, patient-reported)

The Evidence — Antioxidant, Anti-Inflammatory, and Anticancer Research

Beyond its circadian role, melatonin has documented antioxidant and anti-inflammatory activity, and a genuine, decades-long body of human trial research on melatonin as an adjunct to conventional cancer treatment. This is more than the laboratory-only mechanism it's sometimes reduced to, but it's also not evidence that melatonin treats cancer on its own, and the section below is written to show both the real signal and the real limitations in this literature honestly.

Mohammadpour Fard R, Rashno M, Bahreiny SS. "Effects of Melatonin Supplementation on Markers of Inflammation and Oxidative Stress in Patients With Diabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials." Clinical Nutrition ESPEN. 2024 Oct;63:530-539. PMID: 39053698. Meta-analysis of 14 randomized, placebo-controlled trials, 823 people with diabetes. Melatonin significantly reduced CRP, TNF-α, IL-1, IL-6, and malondialdehyde (a marker of oxidative lipid damage), and significantly increased total antioxidant capacity, glutathione, and superoxide dismutase, the body's own antioxidant machinery. This is real human evidence for melatonin's antioxidant and anti-inflammatory effects, specifically in people with diabetes rather than the general population.

Meta-analysis of 14 RCTs (N=823, diabetic patients) Endpoint: Biomarker (inflammatory and oxidative stress markers)

Cao Y, Zhang H, Chen X, Li C, Chen J. "Melatonin: A Natural Guardian in Cancer Treatment." Frontiers in Pharmacology. 2025 Jul 18;16:1617508. PMID: 40756978. Narrative review of melatonin's laboratory anticancer mechanisms: antioxidant activity, inhibition of tumor cell proliferation, migration, and angiogenesis, induction of tumor cell apoptosis, and modulation of epigenetic regulation, metabolic reprogramming, the immune microenvironment, and PI3K/AKT signaling, plus enhanced anticancer activity when melatonin is combined with chemotherapy agents including cisplatin, 5-fluorouracil, and paclitaxel in laboratory and animal models.

Narrative mechanistic review, no clinical trial data Endpoint: Preclinical mechanism (signaling pathways, chemotherapy synergy in lab and animal models)

Mills E, Wu P, Seely D, Guyatt G. "Melatonin in the Treatment of Cancer: A Systematic Review of Randomized Controlled Trials and Meta-Analysis." Journal of Pineal Research. 2005 Nov;39(4):360-366. PMID: 16207291. Meta-analysis of 10 randomized trials, 643 patients with solid tumor cancers, melatonin used as an adjunct to chemotherapy, radiotherapy, or other standard treatment. Melatonin reduced the risk of death at 1 year (relative risk 0.66, 95% CI 0.59–0.73), consistently across melatonin dose and cancer type, with no severe adverse events reported.

Every included trial was conducted at the same hospital network and none were blinded. The authors state this plainly and call for independently conducted, blinded trials to confirm the finding before treating it as settled. That call is what the review below was written to answer.

Meta-analysis of 10 RCTs (N=643), single hospital network, unblinded Endpoint: Clinical outcome (1-year survival)

Yu ZY, Peng RY, Cheng N, Wang RT, Nan MD, Milazzo S, Pilkington K, Seely D, Horneber M, Liu JP. "Melatonin in Cancer Treatment." Cochrane Database of Systematic Reviews. 2025 Apr 30;4(4):CD010145. PMID: 40304216. The current, most comprehensive answer to the trial above: 30 randomized trials, 5,093 patients with cancer, across at least 10 countries. Only 2 of the 30 trials were rated low risk of bias; 28 were rated high risk. Added to standard treatment, melatonin likely reduces fatigue (relative risk 0.46, 95% CI 0.39–0.55, moderate-certainty evidence) and may reduce nausea (low-certainty evidence). On survival specifically, the reviewers write that their results "are consistent with these other reviews in finding that melatonin may increase the one-year survival rate," but rate that evidence very uncertain, and note directly that "one research group did a lot of work on the effect of melatonin on survival, and published many studies," and that this review, like the others before it, is built substantially on that group's trials.

The survival finding and the single-research-group problem are the same finding. The large majority of the trials measuring overall survival and tumor response, in the 2005 meta-analysis above and still in this 2025 update, come from one prolific Italian research group (Lissoni and colleagues) spanning three decades. That doesn't make the finding false, but it does mean it hasn't yet been independently replicated at the scale the original authors themselves called for, and the current Cochrane authors conclude that "the decision for or against using melatonin as an adjunct to cancer treatment cannot easily be made at the current time."

Cochrane review of 30 RCTs (N=5,093), 2 of 30 low risk of bias Endpoint: Clinical outcome (survival, tumor response, fatigue, nausea, quality of life)

None of this is a basis for using melatonin to treat cancer on its own, or a treatment recommendation from this practice. Every trial above used melatonin alongside standard chemotherapy, radiotherapy, or surgery, never in place of it, and the authors of the most current, most rigorous review of this evidence conclude the overall certainty is too low to guide a treatment decision either way. Anyone undergoing cancer treatment who is considering melatonin should raise it with their oncology team, not decide based on a summary page like this one.

What's Reported in Practice

Anecdotal / clinical experience, not yet trial-tested

Patients most often bring up melatonin for occasional difficulty falling asleep, travel across time zones, and adjusting to a shift-work schedule, uses that line up reasonably well with where the trial evidence is strongest. Reports of a noticeably sedating effect, rather than the modest sleep-onset and circadian-timing benefit the trials describe, are common and are probably explained at least partly by supplement doses and formulations that run well above what most trials tested, discussed below. Broader claims tied to melatonin's antioxidant properties, general anti-aging or immune support, are heard often but remain speculative extrapolations from the mechanistic research above, not something with human clinical trial support behind it yet.

What the Research Doesn't Yet Show

Erland LA, Saxena PK. "Melatonin Natural Health Products and Supplements: Presence of Serotonin and Significant Variability of Melatonin Content." Journal of Clinical Sleep Medicine. 2017 Feb 15;13(2):275-281. PMID: 27855744. Laboratory analysis of 31 commercial melatonin supplements. Measured melatonin content ranged from -83% to +478% of the labeled amount, and lot-to-lot variation within a single product reached 465%. More than 71% of supplements fell outside a 10% margin of their label claim, and 26% contained detectable serotonin, a related, controlled substance not disclosed on the label.

Lab analysis of 31 commercial supplements Endpoint: Product quality (measured vs. labeled melatonin content)

Taken together, the gaps here are less about whether melatonin does anything, it clearly affects sleep timing and, more modestly, sleep quality, and more about precision. The sleep evidence itself describes a real but modest effect, smaller than what a prescription hypnotic or an orexin antagonist produces, so it's not a substitute for treating a significant sleep disorder. Layered on top of that modest effect is a supply chain with no requirement that the dose on the label matches the dose in the capsule, which means two people taking "the same" over-the-counter product may not be taking the same thing at all, a problem prescription thyroid hormone and DHEA formulations discussed elsewhere on this site don't share. And the antioxidant and anticancer research, while mechanistically active and worth watching, has not yet produced the human oncology trial data that would justify treating it as anything more than an early research direction.

Whether melatonin fits your situation, and at what dose, timing, and formulation, is an individualized clinical decision made with your provider, particularly if you take warfarin, have a seizure disorder, or are considering it alongside other therapies discussed at your visit.

Next Step

This page covers mechanism and evidence. Dosing, formulation, and whether this is appropriate for you are individual clinical decisions made with your provider.

Already a patient? Bring this up at your next 4Ever Young visit. Have a question first?

Linktree DM on Instagram Email Dr. Wilcox