Drug interactions
Belladonna alkaloids + Diphenhydramine
Severity: Moderate
Belladonna alkaloids 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
Belladonna alkaloids are antimuscarinic agents, and diphenhydramine has strong anticholinergic effects. Together they can cause excessive anticholinergic toxicity, including dry mouth, urinary retention, constipation, tachycardia, blurred vision, confusion and hyperthermia.
What this interaction means in plain words
Belladonna alkaloids 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.
Why it happens
Additive muscarinic receptor antagonism.
What to do
Monitor for anticholinergic toxicity and avoid the combination in older adults or those with glaucoma, urinary retention or ileus. Use a non-sedating antihistamine if one is needed.
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 Belladonna alkaloids with Diphenhydramine?
MediHelp rates the interaction as moderate. Belladonna alkaloids 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. Belladonna alkaloids are antimuscarinic agents, and diphenhydramine has strong anticholinergic effects. Together they can cause excessive anticholinergic toxicity, including dry mouth, urinary retention, constipation, tachycardia, blurred vision, confusion and hyperthermia.
How serious is the interaction between Belladonna alkaloids 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: Monitor for anticholinergic toxicity and avoid the combination in older adults or those with glaucoma, urinary retention or ileus. Use a non-sedating antihistamine if one is needed.
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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