Drug interactions
Diphenhydramine + Tolterodine
Severity: Moderate
Diphenhydramine and Tolterodine: 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 combining them adds to anticholinergic burden. Patients may develop marked dry mouth, constipation, urinary retention, blurred vision, confusion and sedation. Older adults are especially vulnerable.
What this interaction means in plain words
Diphenhydramine and Tolterodine 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.
Diphenhydramine belongs to Respiratory; Tolterodine belongs to Genitourinary.
Why it happens
Additive antimuscarinic pharmacodynamic effects.
What to do
Avoid regular use of sedating antihistamines with tolterodine, especially in older patients, and use a non-sedating antihistamine if one is needed. Monitor for cognitive effects 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 Tolterodine
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Tolterodine?
MediHelp rates the interaction as moderate. Diphenhydramine and Tolterodine 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 combining them adds to anticholinergic burden. Patients may develop marked dry mouth, constipation, urinary retention, blurred vision, confusion and sedation. Older adults are especially vulnerable.
How serious is the interaction between Diphenhydramine and Tolterodine?
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 regular use of sedating antihistamines with tolterodine, especially in older patients, and use a non-sedating antihistamine if one is needed. Monitor for cognitive effects and urinary retention.
What other medicines interact with Tolterodine?
MediHelp also lists interactions of Tolterodine with, for example, Clarithromycin, Clozapine, Cobicistat. The full list is on the Tolterodine page.
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