Drug interactions
Diphenhydramine + Trospium chloride
Severity: Moderate
Diphenhydramine and Trospium chloride: 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 drugs block muscarinic receptors, so their anticholinergic effects add together. This can produce dry mouth, constipation, urinary retention, tachycardia and blurred vision, and may worsen cognition in older adults.
What this interaction means in plain words
Diphenhydramine and Trospium chloride 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.
Why it happens
Additive antimuscarinic pharmacodynamic effects.
What to do
Monitor for anticholinergic adverse effects, especially urinary retention and constipation. Consider a non-anticholinergic alternative to diphenhydramine, particularly in older patients.
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 Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Trospium chloride?
MediHelp rates the interaction as moderate. Diphenhydramine and Trospium chloride 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 drugs block muscarinic receptors, so their anticholinergic effects add together. This can produce dry mouth, constipation, urinary retention, tachycardia and blurred vision, and may worsen cognition in older adults.
How serious is the interaction between Diphenhydramine and Trospium chloride?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for anticholinergic adverse effects, especially urinary retention and constipation. Consider a non-anticholinergic alternative to diphenhydramine, particularly in older patients.
What other medicines interact with Diphenhydramine?
MediHelp also lists interactions of Diphenhydramine with, for example, Alfentanil, Belladonna and opium, Benzhydrocodone / acetaminophen. The full list is on the Diphenhydramine page.
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