What is chlorphenamine? A Guide to this First-Generation Antihistamine

October 11, 2025 •

3 min read

Chlorphenamine, also known as chlorpheniramine, is a first-generation antihistamine that has been used for decades to treat allergy and cold symptoms. In 2023, it was still a commonly prescribed medication in the United States, demonstrating its continued relevance in modern medicine despite its older-generation status.

Quick Summary

Chlorphenamine is a first-generation antihistamine that treats symptoms of allergies and the common cold. It works by blocking histamine receptors in the body, but it is also known to cause side effects such as drowsiness and dry mouth.

Key Points

First-Generation Antihistamine: Chlorphenamine, also known as chlorpheniramine, is a first-generation antihistamine that can cause significant drowsiness.
Blocks Histamine: It primarily blocks histamine receptors to relieve allergy symptoms like sneezing and itching.
Treats Allergies and Colds: Used over-the-counter for allergic rhinitis and cold symptoms such as a runny nose.
Causes Common Side Effects: Frequent side effects include dry mouth, blurred vision, constipation, and dizziness, in addition to drowsiness.
Numerous Drug Interactions: It interacts with alcohol, CNS depressants, and MAOIs, increasing the risk of adverse effects.
Cautions for Specific Groups: Use with caution in older adults and avoid if you have certain medical conditions like glaucoma or an enlarged prostate.
Different Formulations: Available as tablets, liquids, and extended-release capsules for various needs.

How Does Chlorphenamine Work?

Chlorphenamine, a first-generation antihistamine, works by blocking histamine's effects in the body. Histamine is released during allergic reactions, causing symptoms like sneezing and itching. By blocking the histamine H1 receptor, chlorphenamine helps prevent these symptoms. Unlike newer antihistamines, chlorphenamine can cross the blood-brain barrier, which often leads to sedation. It also has weak anticholinergic properties, contributing to side effects like dry mouth and blurred vision.

Common Uses and Applications

Chlorphenamine is frequently used to manage symptoms of allergies and colds and is available over-the-counter.

Allergic rhinitis (Hay Fever): Relieves sneezing and a runny nose.
The common cold: Reduces sneezing and a runny nose.
Urticaria (Hives): Helps ease itching and redness.
Conjunctivitis: Decreases redness and itching of the eyes due to allergies.

It comes in various forms, including tablets and liquids, for different needs.

Dosage and Administration

Appropriate use of chlorphenamine involves following instructions on the product label or the guidance of a healthcare professional. Various formulations exist, such as immediate-release and extended-release, which influence how often the medication is taken. Liquid forms require accurate measurement using a suitable device.

Potential Side Effects and Precautions

Drowsiness is a common side effect of chlorphenamine due to its first-generation nature.

Common Side Effects:

Drowsiness, dizziness, sedation
Dry mouth, nose, throat
Nausea, vomiting, constipation
Blurred vision
Feeling restless or nervous

Serious Side Effects:

Severe dizziness or confusion
Difficulty urinating
Fast or uneven heartbeat
Allergic reactions like hives or facial swelling

Avoid activities requiring alertness until you know how the medication affects you. Do not drink alcohol, as it can worsen drowsiness.

Chlorphenamine vs. Second-Generation Antihistamines

First and second-generation antihistamines differ in their sedative effects and duration. Below is a comparison:


Feature	Chlorphenamine (First-Generation)	Second-Generation Antihistamines (e.g., Cetirizine)
Sedative Effects	High potential for drowsiness	Non-drowsy or low potential for sedation
Onset of Action	Works within about two hours	Often provides faster relief
Duration of Action	Shorter duration	Longer-acting, often providing 12-24 hours of relief
Blood-Brain Barrier	Crosses the blood-brain barrier	Does not cross the blood-brain barrier to a significant extent
Uses	Allergies, colds, urticaria	Primarily for allergies and hives
Interaction with Alcohol	Significant potentiation of CNS depressant effects	Less significant interaction

Who Should Avoid Chlorphenamine?

Chlorphenamine is not suitable for everyone due to potential side effects and interactions.

Children under 6: Safety not established.
Older adults: Increased risk of side effects like dizziness.
Individuals with glaucoma: Risk of increased eye pressure.
People with an enlarged prostate: Can worsen urinary issues.
Patients with asthma or other breathing problems: Can increase chest congestion.
Pregnant or breastfeeding women: Consult a doctor before use.
Individuals taking MAOIs: Risk of dangerous interactions.

Drug Interactions to Be Aware Of

Chlorphenamine interacts with other substances that cause CNS depression.

Substances that interact with chlorphenamine:

Alcohol: Greatly increases sedative effects.
CNS Depressants: Includes sleeping pills and anxiety medications.
MAOIs: Including certain antidepressants.
Certain antibiotics: Consult a pharmacist.

Conclusion

Chlorphenamine is a long-standing first-generation antihistamine effective for managing allergy and cold symptoms by blocking histamine. However, its significant drowsiness sets it apart from newer options. It's not suitable for young children and requires caution for older adults and those with conditions like glaucoma or enlarged prostate. Be aware of interactions with alcohol and other depressants. Understanding its effects and risks helps in deciding if chlorphenamine is appropriate.

NIH National Library of Medicine - Chlorpheniramine, an Old Drug with New Potential Clinical Applications

Frequently Asked Questions

Chlorphenamine is a first-generation antihistamine known for causing drowsiness. Second-generation antihistamines (like cetirizine) are typically non-drowsy and longer-acting as they don't cross the blood-brain barrier as easily.

Avoid driving or operating heavy machinery until you know how chlorphenamine affects you, as drowsiness is a common side effect that can impair your judgment and reactions.

It is generally not advised for children under 6 unless a doctor recommends it. For children 6 and older, follow dosage instructions carefully.

Combining alcohol with chlorphenamine significantly enhances sedative effects, increasing the risk of dizziness, drowsiness, and poor coordination.

Well-known brand names include Chlor-Trimeton and Piriton. It is also found in many combination cold and allergy products.

Chlorphenamine usually starts working within two hours after taking it orally and provides relief for roughly 4 to 6 hours, depending on the specific product.

While it can help with associated symptoms like a runny nose, chlorphenamine is not a cough medicine and does not address the cause of a cough. It might also increase chest congestion.