Drug interactions
Diphenhydramine + Donepezil transdermal
Severity: Moderate
Diphenhydramine and Donepezil transdermal: 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
Donepezil increases acetylcholine by inhibiting cholinesterase, whereas diphenhydramine blocks muscarinic receptors. The anticholinergic drug can reduce the cognitive benefit of donepezil and may worsen confusion in patients with dementia. The combination is generally best avoided.
What this interaction means in plain words
Diphenhydramine and Donepezil transdermal 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
Pharmacodynamic antagonism between cholinesterase inhibition and muscarinic receptor blockade.
What to do
Avoid diphenhydramine in patients taking donepezil and choose a non-anticholinergic alternative. Review cognition and behavior if an anticholinergic must be used.
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 Donepezil transdermal?
MediHelp rates the interaction as moderate. Diphenhydramine and Donepezil transdermal 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. Donepezil increases acetylcholine by inhibiting cholinesterase, whereas diphenhydramine blocks muscarinic receptors. The anticholinergic drug can reduce the cognitive benefit of donepezil and may worsen confusion in patients with dementia. The combination is generally best avoided.
How serious is the interaction between Diphenhydramine and Donepezil transdermal?
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 diphenhydramine in patients taking donepezil and choose a non-anticholinergic alternative. Review cognition and behavior if an anticholinergic must be used.
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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