Melatonin (Circadin)
Is It Right for You?
A complete guide to Melatonin (Circadin) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Melatonin (Circadin)?
Melatonin is an endogenous neurohormone produced by the pineal gland, synthesised from serotonin in response to darkness and suppressed by light exposure. Circadin is the licensed prolonged-release formulation of melatonin 2 mg, formulated to mimic the physiological nocturnal rise in endogenous melatonin that promotes sleep onset and maintenance. It is the only form of melatonin with a UK marketing authorisation as a prescription medication.
Circadin is distinct from the unregulated melatonin supplements widely available online; as a licensed medicine, its dose, release profile, quality, and clinical evidence base have been scrutinised by regulatory authorities. It is licensed specifically for the short-term treatment of insomnia in adults aged 55 and over, where the decline in endogenous melatonin secretion associated with ageing is a contributing factor to sleep disturbance.
Melatonin (Circadin) is a prescription-only medication in the UK in adults. Its use in children is off-label but widely employed under specialist paediatric and paediatric neurology supervision, particularly in children with neurodevelopmental conditions.
What Conditions Is Melatonin Used For?
Melatonin is indicated for:
short-term treatment (up to 13 weeks) of poor sleep quality where sleep onset, sleep maintenance, or overall sleep quality is the principal complaint, and where non-pharmacological measures have been inadequate
resynchronisation of the circadian rhythm following transmeridian travel; most effective for eastward travel involving crossing five or more time zones
shifting the sleep-wake cycle earlier in patients with a pathologically delayed circadian rhythm (off-label, commonly used under specialist direction)
Melatonin does not induce sleep through sedation in the manner of hypnotics (benzodiazepines or Z-drugs). It works by signalling darkness to the brain and advancing the circadian clock, making the body more receptive to sleep at the appropriate biological time. It should be taken at a consistent time in the evening and used alongside good sleep hygiene practices for maximum benefit.
How Does Melatonin Work?
Melatonin's sleep-promoting and circadian-regulating effects are mediated through specific membrane receptors in the brain's principal circadian pacemaker:
MT1 and MT2 receptor agonism: Melatonin binds to high-affinity G-protein-coupled MT1 and MT2 receptors located in the suprachiasmatic nucleus (SCN) — the master circadian clock located in the hypothalamus. MT1 receptor activation suppresses neuronal firing in the SCN, reducing the alerting signals that the circadian system generates during the biological day — thereby reducing wakefulness and promoting sleep onset. MT2 receptor activation plays a principal role in phase-shifting the circadian clock, allowing melatonin to advance or delay the timing of the sleep-wake cycle.
Circadian signal of darkness: Melatonin secretion from the pineal gland is tightly coupled to the light-dark cycle via retinohypothalamic projections. In ageing, pineal melatonin secretion declines substantially — sometimes to levels insufficient to adequately signal the biological night. Circadin's prolonged-release profile supplements this deficient signal, re-establishing the nocturnal melatonin peak that the ageing pineal gland can no longer reliably produce.
No direct sedative effect: Unlike benzodiazepines (which potentiate GABA inhibition) or antihistamines (which cause sedation via H1 blockade), melatonin does not produce pharmacological sedation. Its sleep-promoting effect is entirely through the circadian system, which is why correct timing of administration is critical to efficacy.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Swallow Circadin tablets whole. Do not crush or chew — the prolonged-release coating is essential to the pharmacokinetic profile that mimics the natural nocturnal melatonin rise.
Take 1–2 hours before your desired sleep time. Timing is critical; melatonin must be taken consistently at the same time each evening to exert its circadian-entraining effect reliably.
Can be taken with or after a light snack. Food slows absorption and may modestly affect the release profile; for consistency, take at the same time relative to meals each night.
Dim the lights for 1–2 hours before taking melatonin. Bright light — particularly blue-spectrum light from screens — suppresses endogenous melatonin secretion and blunts the effect of exogenous melatonin. Reducing light exposure in the evening maximises the signal strength.
Use alongside good sleep hygiene. Melatonin is most effective when combined with consistent sleep schedules, avoidance of caffeine after midday, a cool and dark bedroom, and avoidance of stimulating activities before bed.
Side Effects of Melatonin
Most side effects are mild and resolve on their own. Serious side effects are rare but require immediate medical attention.
- Headache --- the most commonly reported adverse effect
- Somnolence or drowsiness the following morning --- particularly in the first few days; usually resolves with continued use
- Dizziness
- Nausea
- Irritability
- Vivid dreams or nightmares
- Dry mouth
- Severe hypersensitivity reactions --- anaphylaxis, angioedema, urticaria; rare
- Worsening depression or mood disturbance --- melatonin can occasionally worsen mood symptoms or trigger dysphoria; report any significant mood changes to your clinician
- Seizure threshold reduction --- rare; isolated reports of seizures in susceptible individuals; use with caution in patients with epilepsy
- Disorientation or confusion --- particularly in elderly patients with cognitive impairment
Some patients experience residual drowsiness the morning after taking Circadin, particularly in the first week of treatment. Patients should exercise caution when driving or operating machinery the morning after taking melatonin until they have established how they personally respond to the medication.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting Melatonin
dramatically increases melatonin plasma levels by inhibiting its principal metabolic pathway; concurrent use significantly increases the risk of adverse effects including excessive sedation; avoid combination.
additive sedative effects; avoid alcohol during melatonin treatment; use other hypnotics concurrently only under clinical guidance.
isolated case reports of potentiated anticoagulant effect; monitor INR if adding melatonin in patients on warfarin.
caffeine may reduce melatonin's sleep-promoting effect by suppressing endogenous melatonin secretion; avoid caffeine after midday during melatonin treatment.
Important Warnings
Patients should assess their personal response to Circadin before driving or operating machinery the morning after taking it. Residual sedation is more common in the early days of treatment and in elderly patients.
Circadin is licensed for use up to 13 weeks. Chronic insomnia beyond this period requires clinical review, reassessment of sleep hygiene and underlying factors, and consideration of longer-term management strategies including cognitive behavioural therapy for insomnia (CBTi), which is the recommended first-line treatment for chronic insomnia.
Melatonin has immunomodulatory properties that may theoretically aggravate autoimmune conditions. Use in patients with autoimmune disease requires specialist consideration.
Isolated reports suggest melatonin may lower seizure threshold in susceptible individuals. Use with caution in patients with epilepsy and monitor for any increase in seizure frequency.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Melatonin FAQs
Endogenous melatonin production declines significantly with age — studies demonstrate that many adults over 55 produce substantially less melatonin at night than younger adults, contributing to age-related insomnia. Circadin's licence reflects the patient population in whom the evidence base was established. Use in younger adults is off-label but may be clinically appropriate in specific circumstances such as delayed sleep phase syndrome or jet lag; your clinician can advise.
Melatonin is not a sedative — it does not directly induce drowsiness by suppressing CNS activity. It works by signalling darkness to the brain's circadian clock, making the appropriate sleep window more biologically receptive to sleep. Patients who expect immediate hypnotic sedation comparable to zopiclone or temazepam will not experience this. Benefits are more subtle — easier sleep onset, improved sleep quality, and better sleep timing — and typically become apparent after 1–2 weeks of consistent use.
Over-the-counter melatonin supplements are not licensed medicines in the UK and are not subject to the same quality, purity, or dose standardisation requirements as Circadin. Studies have found that supplement melatonin content frequently does not match the label, and release profiles vary unpredictably. Circadin is a regulated, clinically evaluated formulation with a specific prolonged-release profile designed to mimic the natural nocturnal melatonin rise.
Yes — melatonin is one of the most evidence-based interventions for jet lag, particularly for eastward travel crossing multiple time zones. Taken at local bedtime at the destination for 2–5 days post-arrival, it accelerates circadian re-entrainment and reduces the duration and severity of jet lag symptoms.
Cognitive behavioural therapy for insomnia (CBTi) is the evidence-based, recommended first-line long-term treatment for chronic insomnia, superior to any pharmacological approach in sustained benefit. It addresses the maladaptive sleep behaviours and thoughts that perpetuate insomnia. Your GP or a referral to a sleep specialist can facilitate access to CBTi, available digitally or in person.