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Melatonin Receptor Agonist — Hypnotic Pregnancy: Insufficient data — avoid unless clearly necessary. Non-pharmacological sleep measures preferred in pregnancy.

Melatonin

Brand names: Circadin (2mg modified-release — licensed), Slenyto (paediatric), Various OTC preparations (unlicensed in UK)

Adult dose

Dose: Insomnia (adults ≥55 years — licensed indication for Circadin): 2mg at bedtime, 1–2h before sleep; take after food. Off-label (adults <55 years, shift work, jet lag): 0.5–5mg at bedtime.
Route: Oral
Frequency: Once nightly, 1–2 hours before bedtime
Max: 2mg OD (licensed Circadin); 10mg (off-label — higher doses not associated with proportionally greater benefit)
Circadin (2mg MR) is licensed only in adults ≥55 years for primary insomnia. Treatment should not exceed 13 weeks. Physiological replacement of endogenous melatonin — no dependence or withdrawal. Non-habit forming — preferred hypnotic in elderly and in patients where benzodiazepine dependence is a concern. Slenyto is licensed for paediatric insomnia associated with autism spectrum disorder (ASD) or Smith-Magenis syndrome.

Paediatric dose

Route: Oral
Frequency: Once nightly, 30–60 minutes before bedtime
Max: 10mg OD (Slenyto — ASD/SMS)
BNFc / NICE: Slenyto: ASD or Smith-Magenis syndrome (2–17 years): 1mg 30–60 min before bedtime; increase to 5mg then 10mg if needed. General paediatric insomnia: off-label use of melatonin 0.5–3mg is widespread — seek specialist paediatric sleep/psychiatry opinion. Not licensed for general insomnia in children under 18 years outside ASD/SMS.

Dose adjustments

Renal

No dose adjustment required.

Hepatic

Significant hepatic impairment: avoid — increased exposure due to reduced hepatic clearance (CYP1A2 metabolism).

Clinical pearls

  • Timing is crucial: take 1–2h before desired sleep time — melatonin signals circadian rhythm shift rather than acting as a direct sedative; taking at the wrong time in the circadian cycle reduces efficacy
  • No dependence — preferred over temazepam or zopiclone for long-term insomnia management in elderly or in patients with prior BDZ dependence
  • Jet lag: take at local destination bedtime for 2–3 days to reset circadian rhythm; 0.5–3mg is adequate (higher doses not more effective for jet lag)
  • Light exposure: advise patients to avoid bright screens and blue light 2h before bedtime — blue light suppresses endogenous melatonin production and counteracts the drug's effect

Contraindications

  • Autoimmune diseases (theoretical — melatonin may stimulate immune function)
  • Hypersensitivity to melatonin

Side effects

  • Headache
  • Somnolence (mild)
  • Dizziness
  • Nausea
  • Irritability (morning residual — rare)
  • No dependence or withdrawal

Interactions

  • Fluvoxamine — strongly inhibits CYP1A2; increases melatonin levels 17-fold; avoid combination
  • CYP1A2 inhibitors (ciprofloxacin, cimetidine) — increase melatonin levels; reduce dose
  • Alcohol — may impair melatonin sleep-promoting effect and increase somnolence
  • Warfarin — possible increased anticoagulant effect; monitor INR

Monitoring

  • Sleep diary (subjective response)
  • No specific blood monitoring required
  • Duration of use (licensed indication for 13 weeks maximum in adults ≥55 years)

Reference: BNFc; BNF 90; NICE NG215 (Insomnia); NICE TA739 (Slenyto for ASD/SMS); Circadin SPC. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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