Melatonin for sleep: the evidence, dosing and the UK rules
Melatonin is a timing signal, not a sedative. Your brain releases it as darkness falls to tell the body clock that night has begun, so taken correctly it shifts when you feel sleepy rather than knocking you out. The evidence is genuinely good for jet lag, delayed sleep phase, some shift workers, older adults and certain children under specialist care, but only modest for ordinary insomnia. Crucially in the UK, unlike the United States, it is a prescription-only medicine, so a clinician should be involved.
Key facts
- In the UK, melatonin is a prescription-only medicine (POM), regulated by the MHRA. It is not sold as a supplement here, unlike in the US.1
- The main licensed product, Circadin 2 mg prolonged-release, is approved only for short-term primary insomnia in adults aged 55 and over.2
- For jet lag, a Cochrane review of ten trials found melatonin 0.5 to 5 mg taken near destination bedtime is effective, with a number-needed-to-treat of about 2.3
- For ordinary insomnia the effect is small: a meta-analysis of 19 trials (1,683 people) found sleep onset shortened by roughly 7 minutes.4
- Timing and dose matter more than size: classic work found 0.3 mg worked better than 3 mg in older adults.5
What melatonin actually is
Melatonin is a hormone made by the pineal gland in the brain. Light hitting the retina suppresses it, so as evening light fades levels climb, peak in the early hours, then fall before waking. This nightly rise is one of the body's main signals for the circadian clock, the roughly 24-hour timer governing sleep, alertness, temperature and hormone release. That is the key idea: melatonin tells your body it is biological night. It does not force sleep the way a sleeping tablet does, which is exactly why it works well for problems of timing but only weakly for plain insomnia. Our piece on the circadian rhythm and how it is reset covers the mechanism in more depth.
Think of melatonin as the dusk signal, not the off switch. A sleeping pill is a hammer; melatonin is a clock that nudges your body's sense of what time it is. This is why a tiny dose at the right hour can beat a large dose at the wrong one.
Where the evidence is genuinely good
Jet lag
This is melatonin's strongest indication. A Cochrane systematic review by Herxheimer and Petrie, covering ten randomised trials, concluded that melatonin is remarkably effective at preventing or reducing jet lag after flights crossing five or more time zones, especially flying east.3 The benefit was clearest when taken close to target bedtime at the destination. Doses between 0.5 and 5 mg worked similarly, and doses above 5 mg were no better. Notably, the review found 2 mg slow-release melatonin relatively ineffective for jet lag, suggesting a brief, higher peak suits this use better than a sustained low level.
Delayed sleep phase and circadian disorders
In delayed sleep-wake phase disorder the body clock runs late, so the person cannot fall asleep until the small hours and struggles to wake for the day. Here melatonin is used as a chronobiotic, a clock-shifter, given in the early evening rather than at bedtime. A meta-analysis found it advanced the body's own melatonin rhythm and brought sleep onset earlier, shortening time to fall asleep by around 23 minutes.6 The trick is timing: a low dose taken a few hours before natural sleep onset moves the clock earlier, whereas the same dose at bedtime mostly just makes you a little drowsy.
Older adults
Natural melatonin output tends to fall with age, which is part of the rationale for the UK licence in the over-55s. Circadin 2 mg prolonged-release is designed to mimic a natural overnight profile and is licensed for short-term primary insomnia in this group.2 Even here the effect is modest, but the safety profile is favourable compared with traditional sleeping tablets.
Shift work
The evidence is weaker and graded low-quality. A Cochrane review found melatonin taken after a night shift may extend daytime sleep by about 24 minutes on average, without clearly helping people fall asleep faster.7 It is a reasonable option for some shift workers but not a reliable fix.
Children with certain conditions
Melatonin is widely prescribed, usually by specialists, for sleep problems in children with neurodevelopmental conditions such as autism and ADHD, where randomised trials show improved sleep latency and duration. This is largely off-label specialist use, not a first step. For otherwise healthy children with insomnia, a 2023 review group recommended that behavioural approaches and cognitive behavioural therapy be tried before melatonin.8
Evidence strength, plainly. Jet lag: good (Cochrane review, multiple RCTs). Delayed sleep phase: moderate, when timed correctly. Older adults: modest but licensed. Shift work: low-quality. Children with neurodevelopmental conditions: moderate but specialist-led. General adult insomnia: weak, with a small effect size.
Where the evidence is weaker: ordinary insomnia
For garden-variety insomnia in healthy adults, melatonin underperforms its reputation. A meta-analysis of 19 randomised, placebo-controlled trials in 1,683 people found it shortened the time to fall asleep by about 7 minutes, increased total sleep by roughly 8 minutes, and produced a small improvement in sleep quality.4 Statistically real, but smaller than most people expect, and smaller than cognitive behavioural therapy for insomnia (CBT-I), which UK guidance treats as first-line for chronic insomnia. Melatonin is best seen as a clock corrector, not a primary insomnia drug.
Why lower doses and correct timing usually win
More is not better. In a classic study by Zhdanova and colleagues, a near-physiological 0.3 mg dose improved sleep in older adults more effectively than 3 mg, while the higher dose pushed blood levels well above the natural range.5 The 3 to 10 mg doses common in US shops often exceed what the receptors need, can leave melatonin circulating into the morning, and may cause next-day grogginess. For shifting the clock, getting the hour right matters more than the milligrams.
| Use | Typical dose and timing | What the evidence shows | Strength |
|---|---|---|---|
| Jet lag | 0.5 to 5 mg at destination bedtime | Reduces jet lag, especially eastward; NNT ~23 | Good |
| Delayed sleep phase | Low dose, hours before natural sleep onset | Advances clock; sleep onset ~23 min earlier6 | Moderate |
| Older adults (55+) | 2 mg PR, 1 to 2 hours before bed | Modest gain; only licensed UK use2 | Modest, licensed |
| Shift work | 1 to 5 mg before daytime sleep | ~24 min more daytime sleep7 | Low-quality |
| General insomnia | Various | Sleep onset ~7 min faster only4 | Weak |
The UK rules: prescription only
This is the point most people get wrong. In the United States melatonin is sold freely as a dietary supplement, so UK readers often assume the same here. They cannot. In the UK it is a prescription-only medicine regulated by the MHRA, prescribed by a doctor and dispensed by a pharmacist.1 The NHS notes it is used mainly for short-term sleep problems in people aged 55 and over, and can be prescribed by specialists for longer-term problems in some children and adults.9 It usually takes 1 to 2 hours to work and is typically prescribed for up to 13 weeks; other uses, including jet lag and most children's prescribing, are often off-label or specialist-initiated. Buying it online from overseas sellers bypasses exactly the clinical oversight that timing-sensitive use needs. For a more freely available alternative, see our guide to magnesium for sleep and stress.
Safety, honestly. Melatonin is generally well tolerated for short-term use. The most common effects are headache, daytime sleepiness, dizziness and nausea.9 Because it can reduce alertness for several hours, the product information advises not driving or using machinery after a dose. Alcohol and other sedating substances increase drowsiness, and there are potential interactions, including with blood thinners such as warfarin. It is generally not recommended in pregnancy, breastfeeding or when trying to conceive due to limited safety data. Report suspected side effects via the MHRA Yellow Card scheme, and never substitute melatonin for treatment your clinician advises.
Who might reasonably use it
On current evidence, melatonin makes most sense for a timing problem: a frequent long-haul traveller crossing several time zones, someone with a genuinely delayed body clock, a shift worker, an older adult with short-term insomnia, or a child with a relevant condition under specialist care. For ordinary insomnia, behavioural treatment (CBT-I) and good sleep habits should come first. If you are new to changing your routine, our getting-started guide explains how to trial one thing at a time so you can tell what actually helps.
What to ask your GP
- Is my problem one of sleep timing (jet lag, delayed clock, shift work) or general insomnia, and does that change whether melatonin is suitable?
- If melatonin is appropriate, what dose and what time of evening should I take it, and immediate or prolonged-release?
- Could it interact with my current medicines, such as blood thinners or sedatives?
- Should I try cognitive behavioural therapy for insomnia (CBT-I) first?
- How long should I take it, and when should we review?
References
- Medicines and Healthcare products Regulatory Agency. Melatonin: prescription-only medicine status and licensed indications. UK regulatory information, accessed 2026. nhs.uk overview.
- European Medicines Agency. Circadin (melatonin 2 mg prolonged-release): summary of product characteristics and indication for primary insomnia in adults aged 55 and over. ema.europa.eu.
- Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev. 2002;(2):CD001520. PMID 12076414.
- Ferracioli-Oda E, Qawasmi A, Bloch MH. Meta-analysis: melatonin for the treatment of primary sleep disorders. PLoS One. 2013;8(5):e63773. journals.plos.org.
- Zhdanova IV, Wurtman RJ, Regan MM, et al. Melatonin treatment for age-related insomnia. J Clin Endocrinol Metab. 2001;86(10):4727-4730. PMID 11600532.
- van Geijlswijk IM, Korzilius HPLM, Smits MG. The use of exogenous melatonin in delayed sleep phase disorder: a meta-analysis. Sleep. 2010;33(12):1605-1614. PMC2982730.
- Liira J, Verbeek JH, Costa G, et al. Pharmacological interventions for sleepiness and sleep disturbances caused by shift work. Cochrane Database Syst Rev. 2014;(8):CD009776. cochranelibrary.com.
- Harderup Larsen LM, et al. Use of melatonin in children and adolescents with idiopathic chronic insomnia: a systematic review, meta-analysis, and clinical recommendation. eClinicalMedicine. 2023;61:102048. thelancet.com.
- NHS. About melatonin: brand names Circadin, Adaflex, Ceyesto, Slenyto, Syncrodin. NHS Medicines A to Z, reviewed 2023. nhs.uk.
This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.