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.
Also called: Chlorpheniramine
Quick facts
- Group
- 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.
Mechanism of action
The figure shows doxepin, a tricyclic first-generation H1 blocker, in the human H1 receptor; chlorphenamine binds the same site.
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 →
- Symptom relief in the common cold, in combination products Common cold (acute viral rhinopharyngitis) →
- Itch and hives 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
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
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.
Connections
← Back to the class: 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 (MedlinePlus (U.S. National Library of Medicine), 2026); Antihistamines - NHS (NHS, 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.