Cyproheptadine

How it works

It antagonises histamine H1 receptors and also blocks serotonin (5-HT2) receptors, which underlies both its antiallergic effects and its use in counteracting excess serotonergic activity.

Prescribing in practice

• Its antimuscarinic and sedative effects make it hazardous in the elderly and in those with conditions such as narrow-angle glaucoma, urinary retention or prostatic enlargement.
• It causes drowsiness, which may impair driving and skilled tasks, and is given orally so requires a patient who can take enteral medication.
• In serotonin syndrome it is used off-label as adjunctive therapy alongside supportive care and withdrawal of the offending agents, per current prescribing references.

Monitoring

Monitor for sedation, antimuscarinic effects and clinical response, particularly when used for serotonin syndrome.

Counselling the patient

• This medicine can make you drowsy; do not drive or operate machinery until you know how it affects you.
• Avoid alcohol, which can increase the drowsiness.
• Tell your clinician about glaucoma or difficulty passing urine before taking it.

Evidence & guidelines

Cyproheptadine is a long-established antihistamine, and its use as an antiserotonergic antidote in serotonin syndrome is supported by toxicology guidance and case experience.