[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [H1 antihistamines](https://durgical.com/en/pharmacology/classes/h1-antihistamines/) › Cyproheptadine

# Cyproheptadine

## H1 antihistamines?

H1 antihistamines

A sedating antihistamine that also blocks serotonin receptors; known for increasing appetite and as an antidote in serotonin syndrome.

Updated Nov 1, 2026

## Quick facts

**Group**
[H1 antihistamines](https://durgical.com/en/pharmacology/classes/h1-antihistamines/)

**Target**
Histamine H1 receptor

**Used for**
Allergic rhinitis · Itchy allergic skin conditions

**Key effects**
Drowsiness · Increased appetite and weight gain

**Monitor**
Sedation · Weight · In serotonin syndrome

**ATC**
R06AX02

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

◎**Histamine H1 receptor**Cyproheptadine

ⓘ The figure shows doxepin, a tricyclic first-generation H1 blocker, in the human H1 receptor; cyproheptadine, also tricyclic, binds the same site.

**Target in 3D:** Histamine H1 receptor. PDB structure 3RZE (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/3RZE) · Drag to rotate · pinch to zoom

Cyproheptadine is a first-generation antihistamine that competes with both histamine (H1) and serotonin (mainly 5-HT2) for their receptors, with anticholinergic and sedative effects. Serotonin blockade is why it is used to treat serotonin syndrome and why it can increase appetite and weight.

- Cyproheptadine blocks H1 receptors: less allergy, sedation
- It also blocks 5-HT2 serotonin receptors
- Serotonin blockade counters serotonin excess and raises appetite
- Muscarinic block adds dry mouth and urinary retention

## Indications

- Allergic rhinitis and allergic conjunctivitis [Allergic rhinitis →](https://durgical.com/en/conditions/allergic-rhinitis/)
- Itchy allergic skin conditions, hives and cold urticaria [Urticaria and angioedema →](https://durgical.com/en/conditions/urticaria-and-angioedema/)
- Add-on after epinephrine in anaphylaxis [Anaphylaxis →](https://durgical.com/en/conditions/anaphylaxis/)
- Serotonin syndrome (off-label antidote) [Serotonin syndrome →](https://durgical.com/en/conditions/serotonin-syndrome/)

## Adverse effects

### Common

- Drowsiness
- Increased appetite and weight gain
- Dry mouth, constipation, blurred vision
- Dizziness

### Serious (rare, important)

- Overdose in infants and young children: hallucinations, seizures, respiratory and cardiac arrest
- Paradoxical excitation in children

## Contraindications

- Newborns and premature infants; breastfeeding
- Therapy with MAO inhibitors
- Angle-closure glaucoma, stenosing peptic ulcer, pyloroduodenal or bladder neck obstruction, symptomatic prostate enlargement
- Elderly, debilitated patients

## Key interactions

**MAO inhibitors**
Prolong and intensify the anticholinergic effects

**Alcohol, benzodiazepines, opioids and other CNS depressants**
Additive sedation and slowed breathing

## What is monitored

- Sedation
- Weight
- In serotonin syndrome: temperature, heart rate, rigidity and clonus

## Administration and safety

- Oral tablets or syrup; in serotonin syndrome the tablets may be crushed and given through a nasogastric tube

## Pregnancy and breastfeeding

Human data are limited; it is contraindicated in breastfeeding and in newborns, and use in pregnancy is weighed with the clinician.

## Nursing care

- Assess sedation and fall risk
- Record weight when given for a long time
- Keep away from children; overdose is dangerous in the young
- Teach not to drive or operate machinery until the effect is known, and to avoid alcohol

## Pharmacokinetics

**Absorption**
Well absorbed by mouth

**Metabolism**
Extensive liver metabolism (glucuronidation)

**Elimination**
Urine, as metabolites

## Memory aid

CYPROheptadine: Cuts Your serotonin, Plus Raises Overeating.

## Test yourself

Think of the answer, then tap the question to see it.

## Besides H1, which receptor does cyproheptadine block that makes it useful in serotonin syndrome?

Serotonin 5-HT2 receptors.

## Which typical side effect of cyproheptadine is sometimes used on purpose?

Increased appetite and weight gain.

## Why is cyproheptadine contraindicated with MAO inhibitors?

MAO inhibitors prolong and intensify its anticholinergic effects.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/cyproheptadine/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 3

- [Diphenhydramine](https://durgical.com/en/pharmacology/diphenhydramine/)
- [Hydroxyzine](https://durgical.com/en/pharmacology/hydroxyzine/)
- [Promethazine](https://durgical.com/en/pharmacology/promethazine/)

## Related conditions 4

- [Allergic rhinitis](https://durgical.com/en/conditions/allergic-rhinitis/)
- [Urticaria and angioedema](https://durgical.com/en/conditions/urticaria-and-angioedema/)
- [Anaphylaxis](https://durgical.com/en/conditions/anaphylaxis/)
- [Serotonin syndrome](https://durgical.com/en/conditions/serotonin-syndrome/)

[← Back to the class: H1 antihistamines](https://durgical.com/en/pharmacology/classes/h1-antihistamines/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - CYPROHEPTADINE HYDROCHLORIDE tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=80e13d3f-f4db-4bb4-95d5-5ac1afa70e7e) (DailyMed (U.S. National Library of Medicine), 2026); [Cyproheptadine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682541.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=R06AX02) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/cyproheptadine/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/cyproheptadine/