Drug interactions
Clemastine + Diphenhydramine
Severity: Moderate
Clemastine 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 sedating antihistamines with anticholinergic activity. Taking them together duplicates therapy and increases drowsiness, impaired psychomotor performance and anticholinergic effects such as dry mouth, urinary retention and confusion, especially in older adults.
What this interaction means in plain words
Clemastine 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.
Clemastine belongs to Respiratory; Diphenhydramine belongs to Respiratory.
Why it happens
Additive central H1-receptor antagonism and muscarinic blockade.
What to do
Avoid using two sedating antihistamines together and choose a single agent. Counsel the patient about driving and operating machinery, and monitor older patients for confusion and urinary retention.
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 Clemastine
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Clemastine with Diphenhydramine?
MediHelp rates the interaction as moderate. Clemastine 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 sedating antihistamines with anticholinergic activity. Taking them together duplicates therapy and increases drowsiness, impaired psychomotor performance and anticholinergic effects such as dry mouth, urinary retention and confusion, especially in older adults.
How serious is the interaction between Clemastine 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 using two sedating antihistamines together and choose a single agent. Counsel the patient about driving and operating machinery, and monitor older patients for confusion and urinary retention.
What other medicines interact with Clemastine?
MediHelp also lists interactions of Clemastine with, for example, Alfentanil, Benzhydrocodone / acetaminophen, Buprenorphine buccal. The full list is on the Clemastine page.
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