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First-generation antihistamine + 5-HT₂A antagonist Pregnancy: US Pregnancy Category B. Animal reproduction studies revealed no evidence of impaired fertility or harm to the fetus at oral or subcutaneous doses up to 32 times the maximum recommended human oral dose, and two studies in pregnant women did not show an increased risk of abnormalities; nevertheless, because human studies cannot rule out the possibility of harm, cyproheptadine should be used during pregnancy only if clearly needed. It is not known whether the drug is excreted in human milk, and antihistamine therapy is contraindicated in nursing mothers.

Cyproheptadine hydrochloride

Brand names: Periactin

Cyproheptadine is a first-generation, sedating antihistamine with additional antiserotonergic activity, used for allergic conditions and pruritus and sometimes for migraine prophylaxis or appetite stimulation.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Initiate with 4 mg (1 tablet) three times a day and adjust according to the size and response of the patient. The therapeutic range is 4 to 20 mg a day, with the majority of patients requiring 12 to 16 mg a day.
Route: Oral
Frequency: Three times a day (initial regimen)
Max: The total daily dose for adults should not exceed 0.5 mg/kg/day (0.23 mg/lb/day). An occasional patient may require as much as 32 mg a day for adequate relief.
SOURCE CAVEAT: no UK SPC (eMC) record was retrieved in this bundle — the dose above is taken from US labelling (Chartwell RX, label date 2023-01-27) and must be verified against the UK SPC before publication. Dosage should be individualised according to the needs and the response of the patient. Contraindicated in elderly and debilitated patients per the US label contraindications. Paediatric age-band doses from the same label: 2 to 6 years — 2 mg (half a tablet) two or three times a day, not to exceed 12 mg a day; 7 to 14 years — 4 mg (1 tablet) two or three times a day, not to exceed 16 mg a day. Safety and effectiveness in children below the age of two years have not been established, and the drug should not be used in newborn or premature infants. In small children for whom calculation of dosage based upon body size is important, cyproheptadine syrup may be needed to permit accurate dosage. Verify all paediatric use against a children's formulary.

Paediatric dose

Dose: 0.25 mg/kg
Route: Oral
Frequency: Total daily dose, given in divided doses (the label's age bands use two or three times a day)
Max: 12 mg a day in children aged 2 to 6 years; 16 mg a day in children aged 7 to 14 years
US label: the total daily dosage for children may be calculated on the basis of body weight or body area using approximately 0.25 mg/kg/day (0.11 mg/lb/day) or 8 mg per square metre of body surface (8 mg/m2). Contraindicated in newborn or premature infants; safety and effectiveness in children below the age of two years have not been established. This figure is from US labelling — verify against the UK SPC and a children's formulary before use.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

US label: the total daily dosage for children may be calculated on the basis of body weight or body area using approximately 0.25 mg/kg/day (0.11 mg/lb/day) or 8 mg per square metre of body surface (8 mg/m2). Contraindicated in newborn or premature infants; safety and effectiveness in children below the age of two years have not been established. This figure is from US labelling — verify against the UK SPC and a children's formulary before use.

Verify in a children's formulary

Contraindications

  • Newborn or premature infants
  • Nursing mothers — antihistamine therapy is contraindicated because of the higher risk of antihistamines for infants, particularly newborns and prematures
  • Hypersensitivity to cyproheptadine and other drugs of similar chemical structure
  • Monoamine oxidase inhibitor therapy
  • Angle-closure glaucoma
  • Stenosing peptic ulcer; pyloroduodenal obstruction; symptomatic prostatic hypertrophy; bladder neck obstruction
  • Elderly, debilitated patients

Side effects

  • Sedation and sleepiness (often transient), dizziness, disturbed coordination, confusion, restlessness, excitation, tremor, insomnia, convulsions, hallucinations
  • Dryness of mouth, epigastric distress, anorexia, nausea, vomiting, diarrhoea, constipation, jaundice
  • Increased appetite and weight gain; fatigue, chills, headache
  • Hypotension, palpitation, tachycardia, extrasystoles, anaphylactic shock
  • Blurred vision, diplopia, vertigo, tinnitus, acute labyrinthitis
  • Urinary frequency, difficult urination, urinary retention, early menses; haemolytic anaemia, leukopenia, agranulocytosis, thrombocytopenia; rash, urticaria, oedema, photosensitivity

Interactions

  • Monoamine oxidase inhibitors — concurrent MAOI therapy is listed as a contraindication (US label CONTRAINDICATIONS, cross-referring to DRUG INTERACTIONS)
  • NOTE: the full drug interactions section was not captured in this bundle; no UK SPC §4.5 is available for this record

Clinical monograph

How it works

It antagonises histamine H1 receptors and serotonin (5-HT) receptors, producing antihistamine, antipruritic, appetite-stimulating and antimigraine effects.

Prescribing in practice

  • It is markedly sedating with antimuscarinic effects, so avoid in narrow-angle glaucoma, urinary retention and prostatic enlargement, and use caution in the elderly because of confusion and falls.
  • Additive sedation and antimuscarinic burden occur with alcohol, other antihistamines, tricyclics and anticholinergics.
  • Its appetite-stimulant and weight-gain effect can be useful in selected patients but is undesirable in others.

Monitoring

Routine laboratory monitoring is not required; review for sedation, anticholinergic effects and, where relevant, weight change.

Counselling the patient

  • Expect drowsiness and avoid driving or operating machinery until you know how it affects you.
  • Avoid alcohol while taking it.
  • Report difficulty passing urine, dry mouth or blurred vision.

Evidence & guidelines

Cyproheptadine is a long-established antihistamine whose sedative and antiserotonergic properties underpin its varied uses.

Reference: TOXBASE / NPIS serotonin syndrome; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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