Melatonin: the sleep hormone peptide stores sell at ten times the trial dose

What is melatonin, and why is it on a peptide comparison site? Melatonin is a small hormone, chemically N-acetyl-5-methoxytryptamine, that the pineal gland makes from the amino acid tryptophan by way of serotonin. Its release rises in the evening as light fades, peaks in the middle of the night and falls towards morning, and that rhythm is the main signal the body uses to tell its internal clock that it is dark. It is an indoleamine, a single small molecule with no amino acid chain, so it is not a peptide in any sense. If you want the definition, our guide to what research peptides are explains what does and does not count.

It appears on PepFinder because peptide stores sell it. The same suppliers that list DSIP, Epitalon and Selank as sleep or calming products often add a melatonin peptide listing next to them, typically as 10 mg or 20 mg capsules, as sublingual or oral drops, and occasionally as a lyophilised vial or a product labelled nasal spray. We list it under Other compounds sold by peptide stores, and we show those listings without ranking them against peptides. This guide covers the evidence behind melatonin for sleep and jet lag, the melatonin side effects reported in trials, the melatonin dosage those trials used, and the regulatory position in each market, which for melatonin varies more than for almost any other product on the site.

Two things make melatonin unusual among the compounds sold by peptide stores. First, it has a genuine, large and largely independent trial record: unlike most research peptides, the melatonin benefits that sellers describe have been tested in randomised, placebo-controlled studies, and the effect sizes are known. Second, the products sold by peptide stores are often several times stronger than anything those trials used, so the research does not describe the product on the shelf as closely as the numbers on the label suggest.

Melatonin acts on two receptors in the brain, MT1 and MT2, that are concentrated in the suprachiasmatic nucleus of the hypothalamus, the cluster of cells that keeps the body clock. Through those receptors it does two separate things. It has a mild direct sleep-promoting effect, which is why an evening dose shortens the time taken to fall asleep, and it has a chronobiotic effect, meaning it shifts the timing of the clock. A dose taken in the early evening, before the body’s own melatonin would normally rise, pulls the clock earlier; a dose taken in the early morning pushes it later. The chronobiotic effect is what matters for jet lag and for delayed sleep phase, and it depends on timing far more than on dose ^[3][7].

Because the body’s own night-time level is low, in the tens of picograms per millilitre of plasma, a very small oral dose is enough to reproduce it. Zhdanova and colleagues showed that 0.3 mg by mouth produces roughly physiological night-time blood levels in older adults, while 3 mg pushes plasma melatonin well above the physiological range and keeps it elevated into the following day ^[6]. That point recurs throughout the literature and is the reason the dosing reviews below keep returning to the lowest dose that works ^[8]. It is also why a 10 mg or 20 mg capsule bears little relation to what the pineal gland does.

Melatonin is also an antioxidant in cell and animal experiments and has been studied for many other conditions, from migraine to critical illness. This guide sticks to the sleep and circadian uses, because those are what the meta-analyses cover and what peptide-store buyers are looking for.

The best-known figures come from a 2013 meta-analysis by Ferracioli-Oda, Qawasmi and Bloch, which pooled randomised placebo-controlled trials of melatonin in primary sleep disorders. Across the pooled trials melatonin shortened sleep onset latency by about 7 minutes, increased total sleep time by about 8 minutes, and produced a small improvement in rated sleep quality. The authors noted that the effects were statistically robust but modest, and that they were smaller than those of prescription hypnotics, with the trade-off that melatonin does not carry the same dependence and next-day impairment problems ^[1].

An earlier meta-analysis by Brzezinski and colleagues in 2005 reached a similar conclusion from a smaller pool of studies: melatonin reduced the time taken to fall asleep by a few minutes, raised sleep efficiency by a small percentage, and modestly increased total sleep time. The authors were careful to describe the effect as real but small, and to say that the clinical meaning of a few minutes’ difference is open to interpretation ^[2].

A 2017 systematic review by Auld and colleagues looked at melatonin across the primary adult sleep disorders and concluded that the strongest evidence is for primary insomnia and for delayed sleep-wake phase disorder, where the chronobiotic effect is doing the work. For other sleep disorders the evidence was thinner or inconsistent. The review’s message is consistent with the meta-analyses: melatonin works, in the sense that trials can detect it against placebo, but the size of the effect on ordinary insomnia is small ^[7].

For melatonin jet lag use, the 2002 Cochrane review by Herxheimer and Petrie is the standard source. It found that most of the included trials showed melatonin, taken close to the target bedtime at the destination, reduced jet lag after flights crossing several time zones, with the clearest benefit on eastward flights. Doses from 0.5 mg to 5 mg appeared similarly effective at reducing jet lag, although people given the higher dose in that range fell asleep faster and slept better. The reviewers judged it effective and safe for occasional short-term use by adult travellers, and said it should be taken on the day of travel and for a few days afterwards ^[3].

None of these reviews found that melatonin helps healthy people who already sleep well sleep more, and none tested the 10 mg and 20 mg products common in peptide stores. The trial record is a record of small doses in people with a sleep complaint.

Age-related insomnia is the best-studied single use, because melatonin output falls with age. Zhdanova and colleagues ran a placebo-controlled crossover study in older adults with insomnia, comparing 0.1 mg, 0.3 mg and 3 mg taken before bed. The 0.3 mg dose, which produced night-time blood levels in the normal young-adult range, improved sleep efficiency, mainly in the middle of the night. The 3 mg dose did not add benefit and was associated with plasma levels far above normal that persisted into the daytime, along with a fall in body temperature. The authors argued for a physiological dose rather than a pharmacological one ^[6].

Vural, van Munster and de Rooij reviewed the dosing evidence in older adults in 2014. Their conclusion was that the lowest dose that works, in an immediate-release form to mimic the normal night-time rise, is the sensible target, and that the useful range in the trials they reviewed sat roughly between 0.3 mg and 2 mg. They found no evidence that larger doses were more effective in this group and noted that higher doses prolong the time the hormone stays elevated ^[8].

The licensed product tells the same story from the regulatory side. Circadin, the prolonged-release tablet licensed by the MHRA and across the EU, contains 2 mg of melatonin and is indicated as monotherapy for the short-term treatment of primary insomnia characterised by poor quality of sleep in patients aged 55 or over. Its summary of product characteristics describes a dose of one 2 mg tablet once daily, taken one to two hours before bedtime and after food, for up to 13 weeks ^[10]. That is the evidence base a medicines regulator was prepared to license, and it is a fraction of the strength of the products in peptide-store listings.

One further human study matters for buyers rather than patients. Erland and Saxena analysed the melatonin content of 31 supplements sold in Canada and found that the actual content ranged from 83% below to 478% above what the label said, that content varied between lots of the same product, and that serotonin, a controlled substance in medicinal form, was present in about a quarter of the products tested. The authors noted that the tested supplements were not being manufactured to a consistent standard ^[4]. There is no equivalent published survey of products sold by peptide stores, so the assumption has to be that the same problem applies at least as often.

The doses in the trials above are small. The primary insomnia meta-analyses pooled studies using a range that mostly ran from under 1 mg up to about 5 mg, with a few higher ^[1][2]. The age-related insomnia trial used 0.1 mg, 0.3 mg and 3 mg and found 0.3 mg the most useful ^[6]. The dosing review in older adults put the practical range at roughly 0.3 mg to 2 mg ^[8]. The jet lag trials used 0.5 mg to 5 mg ^[3]. The licensed UK medicine is 2 mg in a prolonged-release tablet ^[10]. Timing was consistent across the studies: melatonin was taken in the evening, shortly before the intended bedtime, and in the jet lag work close to the target bedtime at the destination rather than the departure clock ^[3].

Set against that, the melatonin dosage in a typical peptide-store listing is 10 mg or 20 mg per capsule. A melatonin 10mg capsule is between three and thirty times the dose the age-related insomnia trial found effective, and five times the licensed medicine ^[6][10]. The trials do not show that these larger doses work better; where they were compared directly, the larger dose added daytime carry-over without adding sleep ^[6]. Anyone reading a product page that quotes the sleep-onset figures from the meta-analyses should note that those figures come from doses a fraction of the size of the product being sold.

These are trial doses and licensed doses, described for context. PepFinder does not give dosing advice, and the melatonin calculator on this site is a reconstitution tool for vials; it does not tell you what to take. Melatonin is also poorly soluble in water, so the assumptions built into peptide reconstitution do not transfer cleanly to a lyophilised melatonin vial, which is one reason we treat such listings with caution.

The melatonin side effects reported in randomised trials are mild and uncommon. Andersen, Gögenur, Rosenberg and Reiter reviewed the safety literature in 2016 and concluded that short-term use is generally safe, with no serious adverse events attributable to melatonin at the doses studied. The most frequently reported effects were dizziness, headache, nausea and sleepiness, all at rates close to placebo. The authors noted that long-term safety data in humans were limited and that there was less information on children and on people with existing illness ^[5]. The Cochrane jet lag review similarly recorded no serious harms, with the most common complaint being daytime sleepiness when the dose was taken at the wrong time ^[3].

The clearest dose-related effect is carry-over. In the older adult trial, 3 mg left plasma melatonin elevated into the daytime and lowered body temperature, effects that were not seen at 0.3 mg ^[6]. Grogginess the next morning is the practical version of that, and it is the effect most likely to appear with the 10 mg and 20 mg capsules sold by peptide stores, since those products have never been tested for it. The Circadin summary of product characteristics lists headache, back pain, nasopharyngitis and arthralgia among the commonly reported reactions in its trials, warns that the tablet may cause drowsiness, and advises against alcohol, which reduces its effect on sleep ^[10].

Two safety issues sit outside the trials. The first is product quality: the Canadian supplement survey found actual content up to several times the label and serotonin in about a quarter of products, so a buyer cannot assume the dose on the capsule is the dose inside it ^[4]. The second is accidental ingestion by children. Lelak and colleagues, writing in the US CDC’s Morbidity and Mortality Weekly Report, found that calls to US poison control centres about paediatric melatonin ingestion rose by 530% between 2012 and 2021, in step with growing sales; most were unintentional ingestions by young children, and although the great majority had no or minor effects, a small number needed hospital care and the report records two deaths ^[9]. High-strength capsules and sweet-flavoured drops in an unlabelled research pouch are a worse version of the products that generated those figures.

Is melatonin legal to buy? The answer depends entirely on where you are, and melatonin is one of the clearest examples on PepFinder of the same molecule being a prescription medicine in one country and a supermarket product in another. See our legal status overview for how we classify each market.

United Kingdom: melatonin is a prescription-only medicine. The MHRA has licensed Circadin 2 mg prolonged-release tablets for the short-term treatment of primary insomnia in people aged 55 and over ^[10], and prescribers also use melatonin off-licence for sleep problems in children and for jet lag. Because it is classified as a medicine, melatonin cannot legally be sold as a food supplement in the UK, and a UK store offering melatonin capsules or drops to the public without a prescription is selling a prescription-only medicine outside medicines law. Is melatonin prescription only in the UK? Yes, in every form, and a research label does not change that.

United States: melatonin is a dietary supplement under the 1994 Dietary Supplement Health and Education Act. It is sold freely in pharmacies and supermarkets, in strengths that commonly reach 10 mg and beyond, in gummies, tablets and drops, with no requirement for pre-market approval and no routine checking of content against label. The variability Erland and Saxena found in Canadian products is generally taken to apply to the US market as well ^[4], and the paediatric ingestion data come from the US ^[9]. A US peptide store selling melatonin is selling a legal supplement, which makes it the one product on such a site that a buyer could equally get from a chemist.

European Union: melatonin is a prescription medicine in most member states, with Circadin authorised centrally by the European Medicines Agency for the same over-55 insomnia indication as in the UK ^[10]. A few member states permit low-dose melatonin, generally under 1 mg or 2 mg, to be sold as a food supplement, and the position differs at national level, so an EU buyer needs to check the rule in their own country rather than assume the UK or US position applies.

Australia: melatonin was prescription-only until 2021, when the Therapeutic Goods Administration moved 2 mg prolonged-release melatonin for adults aged 55 and over to Schedule 3, meaning it can be supplied by a pharmacist without a prescription for that group. Other strengths and other uses remain prescription-only. Canada: melatonin is regulated as a natural health product and sold over the counter with a natural product number; the Erland and Saxena survey of Canadian products is the best published evidence of what that market actually contains ^[4].

Sport: melatonin is not on the World Anti-Doping Agency Prohibited List, so athletes may use it, though an athlete buying from a peptide store takes on the risk that the product contains something other than melatonin.

Melatonin is a stable solid at room temperature but degrades on exposure to light, so licensed products are supplied in opaque blister packs or amber bottles and should be kept in their original packaging, dry and out of direct light. Capsules and tablets do not need refrigeration. Liquid drops and sprays are more vulnerable, both to light and to microbial growth once opened, and should be used within the period the label states.

A lyophilised melatonin vial, where a store offers one, is not the same as a peptide vial. Melatonin is poorly soluble in water, and bacteriostatic water is chosen for peptides, not for indoleamines, so the general advice in our peptide storage guide about reconstituting and refrigerating peptides does not carry over. There is no clinical route by which a person would inject melatonin at home, and none of the human evidence above used injection. A vial of melatonin sold for research purposes is, in practice, a solid that will need a solvent other than water, and a listing that presents it as a peptide to be reconstituted should be treated as a warning sign about the seller rather than a feature of the product.

The obvious comparison is DSIP, delta sleep-inducing peptide, which peptide stores sell for the same purpose. The difference in evidence is stark. Melatonin has meta-analyses of randomised trials with measured effect sizes ^[1][2], a Cochrane review ^[3] and a licensed medicine ^[10]. DSIP has a handful of small, mostly old human studies with inconsistent results and no licensed product anywhere. Melatonin’s effect on sleep is small but demonstrated; DSIP’s is not demonstrated at all. Melatonin is also a small molecule that survives swallowing, whereas DSIP is a peptide that would be digested if taken by mouth.

Epitalon is often sold alongside melatonin because both are linked to the pineal gland: Epitalon is claimed to restore pineal melatonin output in older people, and the claim rests on Russian studies that have not been independently replicated. If the goal is raising night-time melatonin, taking a small dose of melatonin itself is the direct and tested route. Selank and Semax are sold for anxiety and cognition rather than sleep, and neither has a sleep trial record comparable to melatonin’s.

Among the other non-peptide compounds on PepFinder, melatonin is closest in character to NAD+, glutathione and L-carnitine: all are naturally occurring molecules with a real supplement market and a trial record that is more measured than the marketing. MK-677, a growth hormone secretagogue that some users take for its effect on deep sleep, is in a different category: it is an unlicensed investigational drug with no supplement status anywhere and a much heavier side-effect profile. Melatonin is the only compound in that group that a UK doctor can prescribe and a US shopper can pick up in a supermarket.

Compared with prescription hypnotics, the meta-analyses are explicit that melatonin’s effect on sleep onset and duration is smaller, but that it lacks the tolerance, dependence and next-day impairment that limit those drugs ^[1]. That is the honest summary of the melatonin benefits: modest, real, and safest at the low doses in which they were shown.

A melatonin for sale listing on a peptide store usually looks like one of four things: a bottle of 10 mg or 20 mg capsules, often 60 or 90 to a bottle; a dropper bottle of sublingual or oral liquid at a stated milligrams per millilitre; a lyophilised vial of a stated total milligram content, styled like a peptide vial; or a small spray bottle labelled nasal spray, which has no supporting trial evidence at all. The capsule and drop products are simply high-strength supplements of the kind sold in the US, and their price per bottle is usually comparable to supplement retailers. The vial and spray products are peptide-store inventions and should be judged as such.

On our melatonin price page we show capsule, drop and spray listings so that you can see what each store charges, but we do not rank them per milligram in the way we compare peptide vials. A per-mg comparison would imply that a 20 mg capsule is better value than a 2 mg tablet, when the trial evidence points the other way, and it would treat a capsule, a liquid and a spray as interchangeable when their absorption differs. Our methodology page and the guide to peptide prices explained set out how the peptide comparisons work and why melatonin sits outside them.

Three checks matter more than price. First, the store: our supplier directory shows which stores publish independent test results, and the guide on how to spot a fake peptide supplier applies as much to a capsule as to a vial. Second, the certificate: melatonin is a small molecule that any analytical lab can quantify by HPLC, so a store that tests its peptides has no excuse for not testing its melatonin; our guides on how to read a peptide COA and third-party peptide testing explain what a genuine certificate shows. Given the published finding that supplement content ranged from far below to nearly five times the label ^[4], a certificate with an actual measured content is worth more for melatonin than for most products. Third, the law in your country: a UK buyer who chooses to buy melatonin from a research store is buying a prescription-only medicine from a seller who cannot lawfully supply it, and a US buyer is paying a peptide store for something a pharmacy sells with better labelling and a returns policy.

If you are in the UK and the reason for buying is insomnia over 55, jet lag or a child’s sleep problem, the products in the trials above are available on prescription, at 2 mg, from a pharmacist who can check interactions and other causes. That is the route the evidence supports. The peptide-store product is a different thing, at a different dose, and this guide has set out where the two diverge.