Cyproheptadine

Key facts

• Cyproheptadine is an antihistamine that also blocks serotonin receptors. It relieves allergy symptoms such as itching and hives, stimulates appetite, and, given by a doctor, can reverse serotonin syndrome, a dangerous drug reaction.
• It's usually taken two to three times a day; effects on appetite and drowsiness are often noticeable within the first days of use.
• It causes marked drowsiness and has anticholinergic effects, so it must be avoided if you have narrow-angle glaucoma, urinary retention, or a bladder outlet obstruction, which it can worsen.
• Seek urgent care for a fast or irregular heartbeat, severe confusion, or swelling of the face, lips, or throat.

What cyproheptadine treats

Cyproheptadine treats allergic conditions such as allergic rhinitis, hives (urticaria), and itching. It is also used, off-label, to stimulate appetite in people who have lost interest in food, including some children and adults with cystic fibrosis or unintended weight loss. In hospital, doctors use it to treat serotonin syndrome, a reaction caused by excess serotonin from certain antidepressants or other serotonergic drugs.

How cyproheptadine works

Cyproheptadine blocks histamine receptors, the target that triggers itching, sneezing, and swelling during an allergic reaction, easing those symptoms. It also blocks serotonin receptors, which increases appetite and, at treatment doses for serotonin syndrome, counters the effects of too much serotonin in the brain.

Before you take it

• Avoid cyproheptadine if you have narrow-angle glaucoma, urinary retention, or a stomach or bladder obstruction; its anticholinergic effects can worsen these.
• It should not be given to newborn or premature infants, who are more sensitive to its effects, including slowed breathing.
• Tell your prescriber about MAOIs, sedatives, or other antihistamines you take; combining them deepens drowsiness and anticholinergic effects.
• Use caution if you are pregnant or breastfeeding, since the drug crosses into breast milk.

Side effects

Common effects are drowsiness, dry mouth, increased appetite, weight gain, and mild dizziness on standing.

Stop and seek urgent medical care for:

• Severe rash or hives.
• A fast or irregular heartbeat.
• Difficulty breathing or swelling of the face, lips, tongue, or throat.
• Marked confusion or hallucinations.

Safety essentials

• Cyproheptadine's anticholinergic effects make it unsafe in narrow-angle glaucoma or urinary retention. Tell your prescriber if you have either condition before starting.
• Drowsiness can be pronounced, especially when treatment starts; avoid driving or operating machinery until you know how it affects you, and avoid alcohol and other sedating medicines.
• Do not give cyproheptadine to newborn or premature infants.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.