Melatonin

Melatonin is a naturally occurring hormone produced mainly by the pineal gland in response to darkness. It is the body's principal chemical signal of night-time and a central regulator of the circadian sleep-wake cycle. Unlike many synthetic research peptides, melatonin is an endogenous hormone that has been studied for decades.

In the United States, melatonin is sold over the counter as a dietary supplement rather than as an approved drug, which shapes how it is regulated, labeled, and marketed. In several other countries it is classified as a prescription medicine. It is important to remember that melatonin is a hormone, not an inert sleep additive.

Melatonin acts primarily through dedicated melatonin receptors that are expressed in the brain and peripheral tissues. High-level themes include:

• Signaling darkness to the circadian clock in the hypothalamus, helping to align internal rhythms with the external light-dark cycle
• Binding melatonin receptors (commonly described as MT1 and MT2) involved in sleep onset and circadian timing
• Acting as a direct and indirect antioxidant that has been studied in laboratory settings

Its role is often described as a timing or "chronobiotic" signal that shifts the phase of the body clock, rather than a classic sedative that forces sleep.

Melatonin is most commonly discussed in the context of circadian disruption, such as jet lag, shift work, and delayed sleep phase patterns, as well as general difficulty falling asleep. Research interest has also extended to its antioxidant properties and various exploratory areas.

Because it is marketed as a dietary supplement in the US, product quality, labeling accuracy, and actual content can vary between brands. Regulatory status differs by country, so any use should be grounded in local regulations and a clear understanding of the difference between supplement marketing and established clinical evidence.

Melatonin is not included on the WADA Prohibited List and is generally permitted for athletes both in and out of competition. It is not classified as a performance-enhancing substance.

As always, athletes subject to testing should verify the current status of any product with their relevant anti-doping authority, since supplement formulations can contain additional ingredients that carry their own considerations.

Commonly reported effects include daytime drowsiness, grogginess, headache, dizziness, and vivid dreams. Because it influences circadian timing, effects can depend heavily on when it is taken relative to a person's own rhythm.

Considerations discussed in the literature include use in children, pregnancy, and people taking other medications, as well as potential interactions. As with any hormone, attention to product sourcing, labeling accuracy, and individual risk factors is important, and high-level summaries cannot substitute for clinical evaluation.

Melatonin is a small, lipophilic hormone that is absorbed and cleared relatively quickly, which is why timing relative to the light-dark cycle is often emphasized in research more than raw quantity.

This information summarizes commonly discussed concepts and does not constitute medical advice or a dosing recommendation.

Melatonin is unusual in this catalog because the same molecule is a supplement in one country and a licensed medicine in another, and the formulations follow that split.

Supplement formats (US). Immediate-release tablets and capsules, sublinguals, liquids, and gummies, in strengths that commonly run from well under 1 mg to 10 mg. Extended-release versions are also sold, on the rationale that a hormone cleared quickly may not cover the second half of the night.

Licensed medicine (EU). Circadin is a 2 mg prolonged-release melatonin tablet authorised across the EU since 29 June 2007 for the short-term treatment of primary insomnia in patients aged 55 and over, taken one to two hours before bed, for up to 13 weeks (EMA EPAR). Note how much narrower that is than the US supplement market's implicit positioning.

Synthetic receptor agonists. Ramelteon and tasimelteon are prescription drugs that act at the same MT1/MT2 receptors but are not melatonin. Ramelteon is one of the agents the American Academy of Sleep Medicine suggests clinicians may use for sleep-onset insomnia — a recommendation it does not extend to melatonin itself (Sateia et al., J Clin Sleep Med 2017).

Blends are where label accuracy degrades. When 25 US melatonin gummy products were analysed, the measured melatonin ranged from 74% to 347% of the labeled quantity, 22 of 25 (88%) were inaccurately labeled, and one contained no detectable melatonin at all but did contain 31.3 mg of CBD (Cohen et al., JAMA 2023). For a compound whose effect depends on getting a small dose at the right time, a threefold label error is not a minor manufacturing detail.

Melatonin has one of the larger evidence bases among sleep-related compounds, with research spanning circadian phase shifting, jet lag, and various sleep endpoints, alongside laboratory work on its antioxidant activity. Results are often described as modest and context-dependent, particularly for its timing effects versus its sedative effects.

Because supplement products vary and study designs differ, claims about melatonin should be interpreted cautiously. High-level overviews are not a substitute for critical appraisal of primary data.

For deeper dives on this hormone, see:

• Melatonin benefits and areas of interest
• Melatonin side effects and safety context
• Melatonin timing concepts (educational)
• Melatonin research and evidence overview

Is melatonin a peptide — and is it the same as Melanotan? No on both counts. Melatonin is an indoleamine: N-[2-(5-methoxy-1H-indol-3-yl)ethyl]acetamide, formula C13H16N2O2, molecular weight 232.3 (PubChem CID 896) — a small molecule built from the amino acid tryptophan via serotonin, not a chain of amino acids. Melanotan I and II are something else entirely: synthetic melanocortin receptor peptides aimed at skin pigmentation and, for MT-II, sexual function. The two share four letters and nothing else — not structure, not receptor, not purpose. Melatonin appears on peptide reference sites mainly because it is a hormone sold over the counter, a rare enough combination to attract the same audience.

Why is it a supplement in the US but a prescription drug elsewhere? Because the two systems classify it differently, not because the molecule differs. In the US melatonin is sold under the dietary supplement framework, which means FDA regulates it less strictly than a prescription or OTC drug (NCCIH). In the EU, prolonged-release melatonin is a licensed medicine with a specific indication and a 13-week limit (EMA, Circadin). The practical consequence is that a US buyer gets far less assurance about what is in the bottle.

How well does melatonin actually work for sleep? Reliably, but modestly. A meta-analysis of 19 randomised trials in 1,683 people found melatonin reduced time to fall asleep by about 7 minutes (weighted mean difference 7.06 min, 95% CI 4.37–9.75) and increased total sleep time by about 8 minutes (8.25 min, 95% CI 1.74–14.75) (Ferracioli-Oda et al., PLoS One 2013). The American Academy of Sleep Medicine's guideline goes further and suggests clinicians not use melatonin for sleep-onset or sleep-maintenance insomnia in adults, a weak recommendation against (Sateia et al. 2017).

Does more melatonin work better? Not necessarily, and there is a direct experiment on this. In adults over 50 with confirmed reduced sleep efficiency, 0.1, 0.3, and 3.0 mg were compared against placebo. The physiologic 0.3 mg dose restored sleep efficiency and raised plasma melatonin into the normal nocturnal range. The 3.0 mg pharmacologic dose also improved sleep, but induced hypothermia and left plasma melatonin elevated into the daylight hours (Zhdanova et al., JCEM 2001) — which, for a molecule whose job is to signal night, is the opposite of what you want at 10 a.m. Common retail strengths sit well above the physiologic range.

Does melatonin help jet lag? This is its strongest use case. A Cochrane review of ten randomised trials found that nine of them showed melatonin, taken close to the target bedtime at the destination (10 p.m. to midnight), decreased jet lag after flights crossing several time zones (Herxheimer & Petrie, Cochrane 2002). Timing relative to destination night is doing the work here, which is consistent with melatonin acting as a clock signal rather than a sedative.

Is melatonin safe for children? This is where the supplement framing has caused measurable harm. US poison centres logged 260,435 pediatric melatonin ingestions between 2012 and 2021, a 530% increase, rising from 0.6% to 4.9% of all pediatric ingestions; five children required mechanical ventilation and two died (Lelak et al., MMWR 2022). Most were unintentional ingestions by children aged five and under, which is a product-format and storage problem as much as a pharmacological one — gummies are indistinguishable from candy.

Is melatonin banned in sport? No. It does not appear on the WADA Prohibited List and is permitted in and out of competition. The caution worth keeping is the label-accuracy one above: what is prohibited is whatever else ends up in a poorly controlled supplement, not the melatonin.