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Melatonin Receptor Agonist Pregnancy: Avoid — melatonin crosses placenta; potential effects on fetal circadian rhythm development; limited human data

Melatonin

Brand names: Circadin (2 mg PR), Slenyto (paediatric)

Adult dose

Dose: 2 mg prolonged-release once nightly 1-2 hours before bedtime
Route: Oral
Frequency: Once nightly
Max: 2 mg/night (Circadin); higher unlicensed doses used in sleep disorders
Short-term insomnia in adults ≥55 years (Circadin) — improves sleep quality and morning alertness; 3-week course; jet lag and shift work are unlicensed indications; do not crush or chew (prolonged-release)

Paediatric dose

Dose: Neurodevelopmental conditions (ASD, ADHD): 2–10 mg nightly (Slenyto 1 mg or 5 mg prolonged-release) mg/kg
Route: Oral
Frequency: Once nightly (30 min before bedtime)
Max: 10 mg/night
Slenyto licensed for insomnia in ASD/Smith-Magenis syndrome ≥2 years; NICE TA739; BNFc

Dose adjustments

Renal

No dose adjustment required

Hepatic

Avoid in severe hepatic impairment — markedly elevated melatonin levels

Paediatric weight-based calculator

Slenyto licensed for insomnia in ASD/Smith-Magenis syndrome ≥2 years; NICE TA739; BNFc

Clinical pearls

  • Circadian rhythm physiology: melatonin is secreted by the pineal gland in response to darkness — peaks at 2-3 AM, suppressed by light; exogenous melatonin administered 1-2h before desired sleep time shifts the circadian phase, reducing sleep-onset latency
  • NICE TA739 (Slenyto): melatonin prolonged-release for insomnia in children with ASD/neurodevelopmental conditions — evidence shows improved sleep onset and total sleep time; important to combine with sleep hygiene and behavioural approaches
  • Adults ≥55 years: Circadin licensed specifically for this age group — reduced endogenous melatonin production with ageing explains benefit; younger adults with insomnia may benefit from short courses but this is unlicensed use
  • Jet lag: low-dose melatonin 0.5-3 mg taken at destination bedtime reduces jet lag symptoms — particularly effective for eastward travel (phase advance); not a licensed indication but widely used and supported by Cochrane review evidence
  • Safety profile: melatonin has minimal abuse potential and no physical dependence — preferred over hypnotic drugs (Z-drugs, benzodiazepines) in older adults where fall/cognitive risks are concerns; MHRA does not classify as controlled drug

Contraindications

  • Autoimmune diseases (caution — melatonin has immunomodulatory effects)
  • Hepatic impairment (severe)

Side effects

  • Headache
  • Nasopharyngitis
  • Back pain
  • Arthralgia
  • Dizziness
  • Somnolence (next-day — minimal with prolonged-release formulation)
  • Mood changes (rare)

Interactions

  • CYP1A2 inhibitors (fluvoxamine) — markedly increase melatonin levels; avoid
  • CYP1A2 inducers (smoking, rifampicin) — reduce melatonin levels; reduced efficacy
  • Warfarin — some evidence of INR increase; monitor

Monitoring

  • Sleep diary (onset latency, total sleep time, quality)
  • Daytime sleepiness assessment
  • No routine laboratory monitoring required

Reference: BNFc; BNF 90; BNFc; NICE TA739 (Slenyto); MHRA SPC Circadin; Herxheimer & Petrie Cochrane Review 2002 (jet lag); ESC/ERS Sleep Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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