Melatonin

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Melatonin is a hormone produced naturally by the pineal gland in the brain in response to darkness.

It plays a central role in regulating the sleep-wake cycle (circadian rhythm), signalling to the body when it is time to sleep and when to wake.

As a medicine, synthetic melatonin is used to treat insomnia and jet lag.

In the United Kingdom, melatonin is classified as a prescription-only medicine (POM), which distinguishes it from many other countries where it is available as an over-the-counter supplement.

The licensed melatonin product in the UK is Circadin, a prolonged-release 2 mg tablet approved for the short-term treatment of primary insomnia in adults aged 55 and over.

Melatonin is also prescribed off-label for other sleep disorders and for children with neurodevelopmental conditions.

Sleep problems are remarkably common in the United Kingdom.

The Great British Sleep Survey found that approximately 30% of adults experience poor sleep regularly, and NHS data indicate that prescriptions for melatonin have risen substantially over the past decade.

Insomnia, defined as persistent difficulty falling asleep, staying asleep, or waking too early despite adequate opportunity for sleep, affects an estimated 10% to 15% of the adult population and becomes more prevalent with age.

This page provides a comprehensive clinical overview of melatonin as a medicine, covering how it works, who it is suitable for, dosage guidance, potential side effects, important safety warnings, and how to obtain a prescription in the United Kingdom.

Important safety information about melatonin

Before reading further, note these essential safety points about melatonin.

• Melatonin is a prescription-only medicine in the UK. Do not purchase unlicensed products from overseas websites without medical advice.
• Circadin (prolonged-release melatonin) is licensed for adults aged 55 and over with primary insomnia for up to 13 weeks.
• Melatonin may cause drowsiness. Do not drive or operate machinery if affected.
• Avoid alcohol while taking melatonin, as it reduces the quality of sleep.
• Tell your prescriber about all medicines you take, especially fluvoxamine, which significantly increases melatonin levels.

Understanding sleep and the circadian rhythm

The circadian rhythm is an internal biological clock that follows an approximately 24-hour cycle, governed primarily by the suprachiasmatic nucleus (SCN) in the hypothalamus.

The SCN receives light signals from the retina via the retinohypothalamic tract and uses this information to synchronise the body's internal clock with the external light-dark cycle.

When light decreases in the evening, the SCN signals the pineal gland to begin producing melatonin.

Rising melatonin levels promote sleepiness, lower core body temperature, and prepare the body for sleep.

Melatonin production is suppressed by light exposure, particularly blue-spectrum light from screens and artificial lighting, which is why exposure to screens before bedtime can delay sleep onset.

As people age, melatonin production naturally declines.

Older adults often produce less melatonin, with a flattened and phase-advanced secretion pattern, contributing to the increased prevalence of insomnia in later life.

This age-related decline provides the biological rationale for using exogenous melatonin to treat insomnia in adults aged 55 and over.

Insomnia is a clinical diagnosis based on difficulty initiating or maintaining sleep, early morning awakening, and associated daytime impairment (fatigue, poor concentration, mood disturbance).

NICE does not have a specific guideline for insomnia management, but the approach recommended by the British Association for Psychopharmacology (BAP) and endorsed by sleep specialists involves addressing sleep hygiene first, offering cognitive behavioural therapy for insomnia (CBT-I) as first-line treatment, and reserving pharmacotherapy for cases where non-pharmacological approaches are insufficient.

How melatonin works: mechanism of action

Exogenous melatonin mimics the action of the naturally produced hormone. It acts primarily on two G-protein-coupled receptors: MT1 and MT2, both located in the suprachiasmatic nucleus.

Activation of MT1 receptors suppresses the SCN's alerting signal, promoting sleep onset.

Activation of MT2 receptors shifts the timing of the circadian clock, which is the basis for melatonin's usefulness in jet lag and circadian rhythm disorders.

MT2 receptor activation also has a role in consolidating sleep during the night.

Circadin uses a prolonged-release formulation that releases melatonin gradually over several hours, mimicking the natural secretion profile (a sustained elevation through the night rather than a sharp peak and rapid decline).

This sustained-release profile is designed to improve both sleep onset and sleep maintenance in older adults.

Immediate-release melatonin preparations (used off-label for jet lag and other indications) produce a sharper peak in blood levels and are more suited to shifting circadian timing or aiding sleep onset alone.

Melatonin is rapidly absorbed after oral administration. The bioavailability of the prolonged-release formulation is enhanced when taken with food.

It is extensively metabolised in the liver, primarily by the cytochrome P450 enzyme CYP1A2, to inactive metabolites that are excreted in the urine.

The elimination half-life of melatonin is approximately 3.5 to 4 hours for the prolonged-release formulation.

Clinical evidence and UK prescribing guidance

The efficacy of prolonged-release melatonin (Circadin) was demonstrated in randomised controlled trials involving adults aged 55 and over with primary insomnia.

In the pivotal studies, Circadin 2 mg taken nightly for 3 weeks significantly improved sleep quality, morning alertness, and quality of life compared with placebo.

The magnitude of benefit was modest (improvements of approximately 15 to 25 minutes in sleep onset latency and 10 to 15 minutes in total sleep time), but the favourable safety profile and absence of dependence risk make it a reasonable option, particularly for older adults in whom benzodiazepines and Z-drugs carry significant risks of falls, cognitive impairment, and dependence.

The BNF lists melatonin under hypnotics and notes the licensed indication of Circadin for primary insomnia in patients aged 55 and over.

It also notes off-label uses, including jet lag and sleep disorders in children with neurodevelopmental conditions.

NICE technology appraisal TA754 recommends Slenyto (prolonged-release melatonin) for insomnia in children and young people aged 2 to 18 with autism spectrum disorder or Smith-Magenis syndrome when sleep hygiene measures have been insufficient.

For jet lag, a Cochrane review found that melatonin taken close to the target bedtime at the destination was effective in reducing subjective jet lag symptoms, particularly after eastward travel across 5 or more time zones.

Doses of 0.5 mg to 5 mg were similarly effective, with 5 mg tending to produce faster sleep onset.

Timing of the dose is more important than the dose itself.

Melatonin compared with other sleep medicines

Understanding how melatonin compares with other options helps inform treatment decisions.

Benzodiazepine hypnotics (temazepam, nitrazepam) enhance GABA activity and are effective at inducing and maintaining sleep, but they carry risks of dependence, tolerance, rebound insomnia, daytime drowsiness, cognitive impairment, and increased fall risk, particularly in older adults.

They are recommended only for short-term use (2 to 4 weeks).

Z-drugs (zopiclone, zolpidem) act on the same GABA-A receptor complex and share similar risks, though they were initially marketed as having fewer problems with dependence.

Current evidence suggests the dependence risk is comparable to benzodiazepines.

Antihistamines (promethazine, diphenhydramine) are available over the counter and may aid sleep onset but cause significant next-day drowsiness and have anticholinergic effects (dry mouth, constipation, urinary retention) that are particularly problematic in older adults.

Melatonin occupies a distinct position among sleep medicines. It does not cause dependence, tolerance, or rebound insomnia.

It has a mild side effect profile and does not impair balance or cognition in the way that benzodiazepines and Z-drugs do, making it a safer option for older adults who are at risk of falls.

The trade-off is that its sleep-promoting effect is more modest than that of traditional hypnotics.

Melatonin is most effective when the underlying problem involves circadian rhythm misalignment rather than severe psychophysiological insomnia.

Who should consider melatonin?

Circadin is licensed for adults aged 55 and over with primary insomnia (insomnia not caused by an underlying medical or psychiatric condition).

Candidates include older adults with difficulty falling asleep or maintaining sleep who have tried sleep hygiene measures and for whom cognitive behavioural therapy is unavailable, impractical, or insufficient.

Melatonin may also be considered for jet lag (particularly when crossing 5 or more time zones eastward), shift work sleep disorder (to help align sleep periods, used off-label), delayed sleep-wake phase disorder (often seen in adolescents and young adults, used off-label), and children with neurodevelopmental conditions and associated sleep disturbance (under specialist supervision).

Side effects of melatonin

Common side effects

Headache, drowsiness, dizziness, and nausea are the most commonly reported side effects. Vivid or unusual dreams may occur. These effects are generally mild and transient.

Uncommon and rare side effects

Irritability, dry mouth, abdominal discomfort, constipation, weight gain, changes in blood pressure, mood disturbance, visual disturbance, and skin reactions have been reported uncommonly. Severe allergic reactions are very rare.

Daytime drowsiness

If you feel drowsy in the morning or during the day, the dose may be too high or the timing too late. Discuss adjusting the dose or timing with your prescriber. Do not drive or operate machinery until drowsiness resolves.

When to seek medical advice

Contact your GP or call NHS 111 if you experience persistent drowsiness, mood changes, or any symptoms that concern you.

Seek emergency medical help (call 999) if you develop signs of a severe allergic reaction (swelling of the face or throat, difficulty breathing).

Report suspected adverse reactions to the MHRA at yellowcard.mhra.gov.uk .

Warnings and precautions

Contraindications and cautions

Melatonin is contraindicated in patients with hypersensitivity to melatonin or any excipient.

Caution is advised in patients with hepatic impairment (melatonin is liver-metabolised), renal impairment, autoimmune disease (theoretical immunomodulatory effects), and epilepsy (conflicting evidence regarding seizure threshold).

Avoid alcohol, as it reduces melatonin's effectiveness on sleep quality. Fluvoxamine markedly increases melatonin levels and should be avoided. Discuss all medications with your prescriber.

Pregnancy and breastfeeding

Melatonin should be avoided during pregnancy due to insufficient safety data. It may be excreted in breast milk; breastfeeding is not recommended during treatment unless advised by a specialist.

How to get melatonin in the UK

Melatonin is available on NHS prescription from your GP or a sleep specialist. Authorised online prescribers registered with the GPhC can also prescribe it after an appropriate consultation.

The NHS prescription charge in England is 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Do not purchase unregulated melatonin products from overseas websites, as quality, purity, and dosing accuracy cannot be guaranteed.

A study published in the Journal of Clinical Sleep Medicine found that the melatonin content of unregulated supplements varied from the labelled dose by as much as 478%, with some products also containing serotonin.

Sleep hygiene: supporting better sleep alongside melatonin

Melatonin works best as part of a broader approach to improving sleep.

Sleep hygiene measures recommended by the NHS and sleep specialists include maintaining a consistent sleep schedule (going to bed and waking at the same time daily, including weekends), creating a dark, quiet, cool bedroom environment, avoiding screens (phones, tablets, computers) for at least 30 to 60 minutes before bedtime, limiting caffeine after midday, avoiding alcohol close to bedtime, taking regular physical exercise (but not within 2 to 3 hours of bedtime), and using relaxation techniques such as mindfulness, progressive muscle relaxation, or guided breathing.

Cognitive behavioural therapy for insomnia (CBT-I) is the most effective long-term treatment for chronic insomnia and is recommended as first-line by sleep specialists and NICE.

NHS Talking Therapies services offer CBT-I in many areas, and validated digital CBT-I programmes (such as Sleepio) are available via the NHS.

Sources

• Circadin 2 mg prolonged-release tablets, Summary of Product Characteristics (EMC)
• Melatonin, British National Formulary (BNF)
• NICE TA754: Melatonin for treating sleep problems in children and young people
• Melatonin, NHS medicines information
• MHRA Yellow Card Scheme