[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/) › Chlorphenamine

# Chlorphenamine

## H1 antihistamines?

H1 antihistamines

A first-generation antihistamine found in many cold and allergy products; it sedates less than diphenhydramine but still causes drowsiness.

Updated Nov 1, 2026

Also called: Chlorpheniramine

## Quick facts

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

**Target**
Histamine H1 receptor

**Used for**
Allergy symptoms · Symptom relief in the common cold

**Key effects**
Drowsiness and slowed reactions · Dry mouth

**Monitor**
Drowsiness · Urinary retention in older men

**ATC**
R06AB04

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**Chlorphenamine

ⓘ The figure shows doxepin, a tricyclic first-generation H1 blocker, in the human H1 receptor; chlorphenamine 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

Chlorphenamine is an alkylamine H1 inverse agonist. It blocks histamine-induced itch, sneezing, secretions and wheals. It crosses into the brain and has mild anticholinergic action, so drowsiness and dry mouth are common, though usually less than with ethanolamines such as diphenhydramine.

- Chlorphenamine binds H1 receptors in the body and brain
- Peripheral block reduces sneezing, itch and secretions
- Central block causes drowsiness
- Mild muscarinic block dries the mouth and nose

## Indications

- Allergy symptoms: sneezing, runny nose, itchy watery eyes [Allergic rhinitis →](https://durgical.com/en/conditions/allergic-rhinitis/)
- Symptom relief in the common cold, in combination products [Common cold (acute viral rhinopharyngitis) →](https://durgical.com/en/conditions/common-cold/)
- Itch and hives [Urticaria and angioedema →](https://durgical.com/en/conditions/urticaria-and-angioedema/)

## Adverse effects

### Common

- Drowsiness and slowed reactions
- Dry mouth, blurred vision and constipation
- Urinary retention, especially with an enlarged prostate
- Dizziness and poor coordination

### Serious (rare, important)

- Paradoxical excitation in children
- Confusion in older adults
- Overdose: anticholinergic toxicity and seizures

## Contraindications

- Hypersensitivity to chlorphenamine
- Young children with over-the-counter cough and cold products
- Caution in angle-closure glaucoma, prostate enlargement or bladder outlet obstruction

## Key interactions

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

**Other anticholinergic drugs (tricyclic antidepressants, oxybutynin, antipsychotics)**
Additive dry mouth, urinary retention, constipation and confusion

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

## What is monitored

- Drowsiness
- Urinary retention in older men

## Administration and safety

- Oral tablets and syrup; an injectable form exists in some countries
- Common ingredient of multi-symptom cold products: check every label for duplicated antihistamines

## Pregnancy and breastfeeding

Chlorphenamine has long pregnancy experience; as with other sedating antihistamines, use near delivery and in breastfeeding is weighed with the clinician.

## Nursing care

- Teach not to drive or operate machinery until the effect is known, and to avoid alcohol
- Ask what other cold or allergy products the patient takes
- Watch older adults for confusion and urinary retention

## Pharmacokinetics

**Absorption**
Well absorbed by mouth

**Metabolism**
Liver

**Elimination**
Urine, mainly as metabolites

**Half-life**
Long and variable, longer in children with kidney or liver disease

## Memory aid

CHLORphenamine is in the COLD-flu combo: one tablet of many, so count the antihistamines.

## Test yourself

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

## To which chemical group of first-generation antihistamines does chlorphenamine belong?

The alkylamines.

## Why is it important to read every label when chlorphenamine is used for a cold?

It is in many combination products, so a patient can take double doses of antihistamine without noticing.

## Which effect is more likely: drowsiness with chlorphenamine or with loratadine?

With chlorphenamine, a first-generation agent that enters the brain.

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

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

## Connections

## Related drugs 3

- [Diphenhydramine](https://durgical.com/en/pharmacology/diphenhydramine/)
- [Pseudoephedrine](https://durgical.com/en/pharmacology/pseudoephedrine/)
- [Dextromethorphan](https://durgical.com/en/pharmacology/dextromethorphan/)

## Related conditions 3

- [Allergic rhinitis](https://durgical.com/en/conditions/allergic-rhinitis/)
- [Common cold (acute viral rhinopharyngitis)](https://durgical.com/en/conditions/common-cold/)
- [Urticaria and angioedema](https://durgical.com/en/conditions/urticaria-and-angioedema/)

[← 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: [Chlorpheniramine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682543.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [Antihistamines - NHS](https://www.nhs.uk/conditions/antihistamines/) (NHS, 2023); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=R06AB04) (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/chlorphenamine/
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