Drug interactions
Chlorpheniramine + Diphenhydramine
Severity: Moderate
Chlorpheniramine and Diphenhydramine: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Both are first-generation antihistamines, so combined use causes excessive sedation and anticholinergic effects including dry mouth, blurred vision, urinary retention and confusion.
What this interaction means in plain words
Chlorpheniramine and Diphenhydramine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Chlorpheniramine belongs to Respiratory; Diphenhydramine belongs to Respiratory.
Why it happens
Additive H1 antagonism with CNS depressant and muscarinic blocking effects.
What to do
Avoid combining the two and use a single antihistamine. Warn patients about drowsiness and avoid use before driving.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Chlorpheniramine
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Chlorpheniramine with Diphenhydramine?
MediHelp rates the interaction as moderate. Chlorpheniramine and Diphenhydramine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Both are first-generation antihistamines, so combined use causes excessive sedation and anticholinergic effects including dry mouth, blurred vision, urinary retention and confusion.
How serious is the interaction between Chlorpheniramine and Diphenhydramine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid combining the two and use a single antihistamine. Warn patients about drowsiness and avoid use before driving.
What other medicines interact with Chlorpheniramine?
MediHelp also lists interactions of Chlorpheniramine with, for example, Belladonna and opium, Benzhydrocodone / acetaminophen, Brexanolone. The full list is on the Chlorpheniramine page.
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