First-generation antihistamine + 5-HT₂A antagonist

Cyproheptadine hydrochloride

Brand names: Periactin

Adult dose

Dose: 4mg TDS (max 32mg/day); serotonin syndrome (off-label): 12mg loading then 2mg q2h

Route: Oral

Frequency: TDS

Clinical pearls

TOXBASE: option for moderate–severe serotonin syndrome alongside supportive care
Off-label appetite stimulant in cachexia, periodic migraine prophylaxis (paediatrics)
Pre-second-generation antihistamine; daytime sedation limits use

Contraindications

Closed-angle glaucoma
Pyloric stenosis
Bladder neck obstruction
Concurrent MAOI
Elderly debilitated patients
Hypersensitivity

Side effects

Sedation
Anticholinergic effects
Weight gain (appetite stimulation)
Dry mouth
Urinary retention

Interactions

MAOIs
Other anticholinergics
Alcohol

Monitoring

Sedation
Weight
Anticholinergic burden

Reference: BNF; TOXBASE / NPIS serotonin syndrome; SmPC; https://bnf.nice.org.uk/drugs/cyproheptadine-hydrochloride/. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways