Drug interactions
Diphenhydramine + Olanzapine / samidorphan
Severity: Moderate
Diphenhydramine and Olanzapine / samidorphan: 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
Olanzapine has anticholinergic activity, and diphenhydramine adds to it, which increases the risk of constipation, ileus, urinary retention and confusion. Additive sedation and orthostatic effects are also possible.
What this interaction means in plain words
Diphenhydramine and Olanzapine / samidorphan 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 and sedative effects.
What to do
Monitor bowel function, urinary symptoms and sedation, and avoid extra anticholinergic drugs where possible. Treat constipation early.
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 Olanzapine / samidorphan?
MediHelp rates the interaction as moderate. Diphenhydramine and Olanzapine / samidorphan 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. Olanzapine has anticholinergic activity, and diphenhydramine adds to it, which increases the risk of constipation, ileus, urinary retention and confusion. Additive sedation and orthostatic effects are also possible.
How serious is the interaction between Diphenhydramine and Olanzapine / samidorphan?
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 bowel function, urinary symptoms and sedation, and avoid extra anticholinergic drugs where possible. Treat constipation early.
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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