Melatonin is a hormone made by the pineal gland in the brain. Its level rises after dark and helps set the timing of the body’s roughly 24-hour clock (circadian rhythm) and of sleep. Synthetic melatonin is taken for sleep problems, jet lag and shift-work schedules, and it has been proposed as a recovery aid for athletes.

The single most important fact is that melatonin’s legal status depends on where you live. In the US it is not an FDA-approved drug. It is sold over the counter as a dietary supplement, in doses and forms that are not checked before sale. In the EU and UK, melatonin medicines such as Circadin are prescription-only, approved for narrow uses such as short-term insomnia in people aged 55 and over.

This page summarizes what regulators, clinical guidelines, trials and product-testing studies report. It is for education only and is not medical advice.

Property	Detail
Class	Endogenous indoleamine hormone; melatonin receptor (MT1/MT2) agonist; ATC code N05CH01
Chemistry	N-acetyl-5-methoxytryptamine, C13H16N2O2, 232.28 g/mol
Approved products	Circadin 2 mg prolonged-release tablet (EU, 2007; UK); Slenyto prolonged-release tablets for children (EU, 2018)
Route	Oral (tablets, capsules, liquids, gummies)
Approved adult dose (Circadin)	2 mg once daily, 1–2 h before bedtime and after food, for up to 13 weeks
Half-life	≈45 min for immediate-release forms (range 28–126 min across studies); 3.5–4 h terminal half-life for Circadin
Oral bioavailability	≈15% (range 9–33%) because of heavy first-pass metabolism in the liver
US status	Dietary supplement; not FDA-approved
EU / UK status	Prescription-only medicine
WADA	Not on the 2026 Prohibited List

What it is

Melatonin is a small indoleamine molecule closely related in structure to serotonin. Its chemical name is N-[2-(5-methoxy-1H-indol-3-yl)ethyl]acetamide (PubChem; Circadin SmPC).

The body’s own melatonin follows a strong daily pattern. According to the Circadin product information, secretion rises soon after darkness, peaks at about 2–4 am and falls during the second half of the night. Light at night suppresses it (NCCIH). Melatonin acts mainly on the MT1 and MT2 receptors, which help regulate circadian timing and sleep (Circadin SmPC).

Because of this, melatonin has two distinct effects that are easy to mix up:

A mild sleep-promoting (hypnotic) effect a short time after a dose.
A clock-shifting (chronobiotic) effect. Taken at the right time, it can move the body clock earlier or later. Taken at the wrong time, it can work against the desired shift (Herxheimer & Petrie, Cochrane 2002).

Supplement melatonin can be made from animal or microbial sources, but it is most often synthetic (NCCIH).

How it works in the body

A systematic review of 22 human pharmacokinetic studies, using doses of 0.3–100 mg, found these typical values (Harpsøe et al., Eur J Clin Pharmacol 2015):

Parameter	Immediate-release oral melatonin
Time to peak level	≈50 min
Elimination half-life	≈45 min (study range 28–126 min)
Oral bioavailability	≈15% (range 9–33%)
Factors that changed exposure	Age, caffeine, smoking, oral contraceptives, food, fluvoxamine

The prolonged-release medicine behaves differently. In the Circadin label, food delayed the peak from 0.75 h to 3.0 h. The terminal half-life is 3.5–4 h, and about 85% of an oral dose is removed by the liver before it reaches the circulation (Circadin SmPC).

Other points from the label:

Metabolism: mainly by the liver enzymes CYP1A1 and CYP1A2 (possibly CYP2C19). The main metabolite, 6-sulfatoxymelatonin, is inactive and is cleared in urine within about 12 hours.
Sex and age: peak levels were 3–4 times higher in women than in men. Older adults (55–69) reached peaks of about 1,200 pg/mL versus about 500 pg/mL in adults aged 18–45.
Liver disease: people with cirrhosis have high daytime melatonin levels, and the label does not recommend Circadin in hepatic impairment.

Very small doses already matter. Cohen and colleagues note that 0.1–0.3 mg can raise blood levels in young adults into the normal nighttime range, far below the 1–10 mg per serving declared on the US gummies they tested (Cohen et al., JAMA 2023).

Regulatory status

United States: dietary supplement

In the US, melatonin is regulated as a dietary supplement, which means the FDA does not review it for safety, effectiveness or dose before it is sold (NCCIH). Melatonin products are not FDA-approved. They are sold over the counter as supplements or food, sometimes combined with ingredients such as cannabidiol (CBD) (Cohen et al., JAMA 2023). US sales rose from $285 million in 2016 to $821 million in 2020 (Lelak et al., MMWR 2022).

European Union: prescription medicine

The European Commission authorized Circadin on June 29, 2007 (EMA). Its approval is narrow:

Indication: short-term treatment of primary insomnia with poor sleep quality, as monotherapy, in patients aged 55 or over.
Dose: one 2 mg prolonged-release tablet daily, 1–2 h before bedtime and after food, for up to 13 weeks.
Supply: prescription only.

Slenyto, a prolonged-release melatonin for children, was authorized on September 20, 2018 (EMA). It is approved for insomnia in children and adolescents aged 2–18 with autism spectrum disorder and/or certain neurogenetic disorders, and aged 6–17 with ADHD, when sleep hygiene measures have not worked. It is also prescription-only.

Separately, EU food law (Regulation 432/2012) authorizes two health claims for foods containing melatonin. One is for jet lag, with at least 0.5 mg per portion. The other is for shortening the time it takes to fall asleep, with 1 mg per portion taken close to bedtime (Regulation (EU) No 432/2012, Annex). These are low-dose food claims. They are not drug approvals.

United Kingdom

In the UK, melatonin is available on prescription only. The NHS lists the brands Circadin, Adaflex, Ceyesto, Slenyto and Syncrodin (NHS). Circadin holds a UK marketing authorization with the same 55-and-over indication as in the EU (Circadin SmPC).

Sport

Melatonin does not appear on the WADA 2026 Prohibited List.

What the research shows

Chronic insomnia: what the AASM guideline says

The American Academy of Sleep Medicine (AASM) 2017 guideline on drug treatment of chronic insomnia in adults suggests that clinicians not use melatonin for sleep onset or sleep maintenance insomnia. This is a WEAK recommendation, meaning low certainty (Sateia et al., J Clin Sleep Med 2017). The same guideline also advised against valerian, tryptophan and diphenhydramine, and suggested ramelteon, a prescription melatonin-receptor drug, for sleep-onset insomnia.

The task force based the melatonin recommendation on three trials of 2 mg prolonged-release melatonin, all in adults over 55. These are the same kind of trials that support Circadin’s European approval:

Trial	n	Duration	Key finding used by AASM
Lemoine	170	3 weeks	Patient-reported outcomes
Luthringer	40	3 weeks	Sleep latency −8.9 min on sleep-lab testing (polysomnography); below the task force’s threshold for clinical significance
Wade	354	3 weeks	Patient-reported outcomes
Pooled (sleep quality)	—	—	Standardized mean difference +0.21 (95% CI −0.36 to 0.77); not clinically significant

The guideline rated the overall evidence quality as very low and judged benefits roughly equal to harms. It also noted that most well-informed patients would probably still choose melatonin over no treatment, because it is widely available and seen as benign.

The Circadin label presents its trials more favorably. In that label, the drug shortened sleep latency by 9 min versus placebo in a sleep-lab study. In an outpatient study, 47% of patients on Circadin improved in both sleep quality and morning alertness, compared with 27% on placebo. A 600-patient trial kept its benefit to 3 months but failed its primary analysis at 6 months (Circadin SmPC).

Pooled trials in primary sleep disorders

A meta-analysis of 19 placebo-controlled trials (1,683 adults and children with primary sleep disorders) found real but small effects (Ferracioli-Oda et al., PLoS One 2013):

Outcome	Melatonin vs placebo (95% CI)
Time to fall asleep	−7.06 min (4.37–9.75)
Total sleep time	+8.25 min (1.74–14.75)
Sleep quality	Standardized mean difference 0.22 (0.12–0.32)

The authors noted that the absolute benefit is smaller than for other insomnia drugs, but that it did not appear to fade with continued use. Longer trials and higher doses showed larger effects on sleep latency and total sleep time.

Circadian rhythm disorders

Melatonin’s best-supported uses are about timing, not sedation. The AASM 2015 guideline on intrinsic circadian rhythm sleep-wake disorders made these recommendations (Auger et al., J Clin Sleep Med 2015):

Condition	AASM 2015 position on strategically timed melatonin
Delayed sleep-wake phase disorder (DSWPD), adults with or without depression	Suggested (WEAK FOR)
DSWPD in children and adolescents, with or without psychiatric conditions	Suggested (WEAK FOR)
Non-24-hour sleep-wake rhythm disorder in blind adults	Suggested (WEAK FOR)
Irregular sleep-wake rhythm disorder in children/adolescents with neurologic disorders	Suggested (WEAK FOR)
Irregular sleep-wake rhythm disorder in older people with dementia	Avoid (WEAK AGAINST)

DSWPD is a condition in which people cannot fall asleep until very late and struggle to wake at normal times. A later double-blind trial randomized 116 patients with DSWPD to 0.5 mg fast-release melatonin or placebo, taken 1 h before their desired bedtime for 4 weeks, together with a fixed bedtime schedule (Sletten et al., PLoS Med 2018). Results:

Sleep onset came 34 min earlier than on placebo (95% CI 8–60 min earlier).
52.8% of patients on melatonin showed more than minimal clinician-rated improvement, versus 24.0% on placebo.
Adverse events (light-headedness, daytime sleepiness, lower libido) occurred at similar rates in both groups.

Jet lag

A Cochrane review of 10 randomized trials found that in 9 of them, melatonin taken close to the target bedtime at the destination reduced jet lag after flights crossing five or more time zones (Herxheimer & Petrie, Cochrane 2002). Its main findings:

Daily doses of 0.5–5 mg worked about equally well. People fell asleep faster and slept better on 5 mg than on 0.5 mg.
Doses above 5 mg were no more effective.
2 mg slow-release melatonin worked relatively poorly, which suggests that a short, higher peak works better for this purpose.
The number needed to treat was 2.
Taking it at the wrong time, early in the day, could cause sleepiness and delay adaptation.

Children

A 2019 review summarized by NCCIH pooled 18 studies in 1,021 children. Melatonin shortened the time to fall asleep and lengthened sleep, with the largest effects in autism spectrum disorder: 37 min faster sleep onset and 48 min more sleep (NCCIH). The studies were small and lasted only 1–13 weeks, so long-term effects on development, including puberty, are unknown.

In a 13-week trial of prolonged-release melatonin in 125 children, total sleep time was 508 min on treatment versus 488 min on placebo (Circadin SmPC). Somnolence and headache were more common on melatonin.

Exercise performance and recovery

A 2026 meta-analysis pooled 19 small randomized trials, with only 266 participants in total, of melatonin versus placebo in athletes and active people (Guo et al., Front Nutr 2026):

Outcome	Standardized mean difference (95% CI)
Explosive power	0.29 (0.05–0.53)
Endurance performance	0.58 (0.29–0.87)
Creatine kinase (muscle-damage marker), reduction	0.59 (0.29–0.89)
Lactate dehydrogenase	0.45 (−0.03 to 0.94); not significant

Effects looked larger with evening dosing more than 6 h before exercise. However, the trials were small and varied in design. The review did not assess muscle growth, and there is no controlled evidence that melatonin is anabolic.

Side effects and risks

Common side effects

In Circadin trials (1,931 patients on drug, 1,642 on placebo), 48.8% of patients on Circadin and 37.8% on placebo reported an adverse event. Adjusted for time on treatment, the rate per 100 patient-weeks was actually lower on Circadin (3.0 vs 5.7). The most common events were headache, nasopharyngitis (cold symptoms), back pain and joint pain, which were frequent in both groups (Circadin SmPC).

Melatonin can cause drowsiness. The label says it has a moderate effect on the ability to drive and use machines. The NHS also lists headache, tiredness, nausea and irritability the next day (NHS).

Interactions

From the Circadin label (SmPC):

Interacting factor	Effect
Fluvoxamine	Exposure (AUC) 17 times higher and peak 12 times higher by blocking CYP1A2/CYP2C19; the label says to avoid the combination
Estrogens (oral contraceptives, HRT), quinolone antibiotics, cimetidine, 5- or 8-methoxypsoralen	Raise melatonin levels
Carbamazepine, rifampicin, cigarette smoking	Can lower melatonin levels (CYP1A2 induction)
Benzodiazepines and Z-drugs (zolpidem, zaleplon, zopiclone)	Added sedation; with zolpidem, worse attention, memory and coordination than zolpidem alone
Alcohol	Reduces melatonin’s effect on sleep

Case reports suggest that people with epilepsy and people taking warfarin may come to harm on melatonin (Herxheimer & Petrie, Cochrane 2002). NCCIH advises that people in these groups use it only under medical supervision (NCCIH).

Who should be cautious

The Circadin label does not recommend melatonin for:

people with liver impairment;
people with autoimmune disease (no clinical data);
pregnancy, or women trying to become pregnant;
breastfeeding.

The AASM advises against melatonin for irregular sleep-wake rhythm in older people with dementia (Auger et al., 2015). NCCIH notes that the long-term safety of melatonin supplements, especially at doses above what the body makes, is not established (NCCIH).

Overdose and children

The Circadin label reports that daily doses up to 300 mg have been described in the literature without clinically significant adverse reactions. Drowsiness is the expected effect of overdose (Circadin SmPC).

Accidental ingestion by children is a growing US problem. US poison centers received 260,435 reports of pediatric melatonin ingestion from 2012 to 2021, and the annual number rose 530% (Lelak et al., MMWR 2022):

By 2021, melatonin accounted for 4.9% of all pediatric ingestions reported, up from 0.6% in 2012.
Over the decade, 4,097 children were hospitalized and 287 needed intensive care.
Five required mechanical ventilation, and two children died.

NCCIH notes that most of these children had no symptoms, and that the poison-center data could not show whether melatonin caused the two deaths (NCCIH).

Quality and label accuracy

Two studies measured how much melatonin over-the-counter products actually contain, and both found that the labeled dose is often wrong.

Erland and Saxena, 2017 (Canada). The researchers tested 31 melatonin supplements from 16 brands bought in grocery stores and pharmacies in Guelph, Ontario (Erland & Saxena, J Clin Sleep Med 2017). They found:

Melatonin content ranged from 83% below to 478% above the label.
More than 71% of products were not within 10% of the label claim.
Content varied by as much as 465% between lots of the same product.
Eight products (26%) contained serotonin, at 1–75 μg, an undeclared contaminant.
The worst outlier was a chewable tablet labeled 1.5 mg that contained almost 9 mg.

Cohen et al., 2023 (US gummies). This study analyzed 25 melatonin gummy products sold in the US (Cohen et al., JAMA 2023):

Finding	Result
Products accurately labeled (within ±10%)	3 of 25 (12%)
Products inaccurately labeled	22 of 25 (88%)
Measured melatonin vs label	74%–347% of the declared amount
Measured melatonin per serving	1.3–13.1 mg
Product with no detectable melatonin	1, which contained 31.3 mg of CBD instead
Products declaring CBD	5, with 104%–118% of the labeled CBD
Serotonin	Not detected

The authors estimated that children taking gummies as directed could be exposed to 40–130 times more melatonin than the 0.1–0.3 mg that raises blood levels into the normal nighttime range.

About “it’s natural, so the dose doesn’t matter.” Melatonin is a hormone the body makes in fractions of a milligram. Supplement doses of 3–10 mg are many times higher, label accuracy is poor, and long-term safety at these doses has not been studied.

Key takeaways

Legal status depends on the country. Melatonin is an unapproved dietary supplement in the US but a prescription medicine in the EU and UK, where Circadin is approved at 2 mg for short-term insomnia in people aged 55 and over.
Weak case for chronic insomnia. The AASM 2017 guideline suggests not using melatonin for chronic insomnia in adults. Pooled trials show it shortens sleep onset by about 7 minutes.
Better for body-clock problems. Timed melatonin has guideline support for delayed sleep phase and for non-24-hour rhythm disorder in blind adults, and good trial evidence for jet lag.
Labels are often wrong. In US gummies, only 3 of 25 products were within 10% of the label, and one contained CBD instead of melatonin.
Interactions and children are the main risks. Fluvoxamine sharply raises melatonin levels, sedatives add to its effect, and accidental pediatric ingestions rose 530% in a decade.
No evidence it is anabolic. Small trials hint at modest performance and muscle-damage benefits, but there is no evidence that it builds muscle.

Sources

RAD Neurim Pharmaceuticals. Circadin 2 mg prolonged-release tablets, summary of product characteristics. emc.
European Medicines Agency. Circadin (melatonin): EPAR, EMEA/H/C/000695. EMA.
European Medicines Agency. Slenyto (melatonin): EPAR, EMEA/H/C/004425. EMA.
NHS. About melatonin. NHS.
National Center for Complementary and Integrative Health. Melatonin: what you need to know. NCCIH.
National Center for Biotechnology Information. Melatonin, PubChem CID 896. PubChem.
Harpsøe NG, Andersen LP, Gögenur I, Rosenberg J. Clinical pharmacokinetics of melatonin: a systematic review. Eur J Clin Pharmacol. 2015;71(8):901–909. PubMed.
Sateia MJ, Buysse DJ, Krystal AD, Neubauer DN, Heald JL. Clinical practice guideline for the pharmacologic treatment of chronic insomnia in adults: an American Academy of Sleep Medicine clinical practice guideline. J Clin Sleep Med. 2017;13(2):307–349. PubMed.
Auger RR, Burgess HJ, Emens JS, et al. Clinical practice guideline for the treatment of intrinsic circadian rhythm sleep-wake disorders: advanced sleep-wake phase disorder (ASWPD), delayed sleep-wake phase disorder (DSWPD), non-24-hour sleep-wake rhythm disorder (N24SWD), and irregular sleep-wake rhythm disorder (ISWRD). An update for 2015. J Clin Sleep Med. 2015;11(10):1199–1236. PubMed.
Ferracioli-Oda E, Qawasmi A, Bloch MH. Meta-analysis: melatonin for the treatment of primary sleep disorders. PLoS One. 2013;8(5):e63773. PubMed.
Sletten TL, Magee M, Murray JM, et al. Efficacy of melatonin with behavioural sleep-wake scheduling for delayed sleep-wake phase disorder: a double-blind, randomised clinical trial. PLoS Med. 2018;15(6):e1002587. PubMed.
Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev. 2002;(2):CD001520. PubMed.
Guo J, Zhou L, Gu J, et al. Timing-dependent effects of melatonin supplementation on exercise performance and exercise-induced muscle damage: a systematic review and meta-analysis. Front Nutr. 2026;13:1742464. PubMed.
Erland LA, Saxena PK. Melatonin natural health products and supplements: presence of serotonin and significant variability of melatonin content. J Clin Sleep Med. 2017;13(2):275–281. PubMed.
Cohen PA, Avula B, Wang YH, Katragunta K, Khan I. Quantity of melatonin and CBD in melatonin gummies sold in the US. JAMA. 2023;329(16):1401–1402. PubMed.
Lelak K, Vohra V, Neuman MI, Toce MS, Sethuraman U. Pediatric melatonin ingestions – United States, 2012–2021. MMWR Morb Mortal Wkly Rep. 2022;71(22):725–729. PubMed.
Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods, Annex. legislation.gov.uk.
World Anti-Doping Agency. The 2026 Prohibited List. WADA 2026 Prohibited List.

Melatonin