Drug interactions
Diphenhydramine + Hyoscyamine
Severity: Moderate
Diphenhydramine and Hyoscyamine: 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 are antimuscarinic, so together they can cause marked dry mouth, constipation, urinary retention, blurred vision, tachycardia and confusion. The risk is highest in older adults and in people with glaucoma or prostatic enlargement.
What this interaction means in plain words
Diphenhydramine and Hyoscyamine 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; Hyoscyamine belongs to Genitourinary.
Why it happens
Additive antimuscarinic receptor blockade.
What to do
Avoid combining in older adults and monitor for anticholinergic toxicity in others. Reduce the dose or stop one agent if symptoms develop.
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
Other interactions of Hyoscyamine
- Amantadine + Hyoscyamine Moderate
- Amitriptyline + Hyoscyamine Moderate
- Aripiprazole + Hyoscyamine Moderate
- Atropine + Hyoscyamine Moderate
- Benztropine + Hyoscyamine Moderate
- Bethanechol + Hyoscyamine Moderate
Frequently asked questions
Can I take Diphenhydramine with Hyoscyamine?
MediHelp rates the interaction as moderate. Diphenhydramine and Hyoscyamine 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 are antimuscarinic, so together they can cause marked dry mouth, constipation, urinary retention, blurred vision, tachycardia and confusion. The risk is highest in older adults and in people with glaucoma or prostatic enlargement.
How serious is the interaction between Diphenhydramine and Hyoscyamine?
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 combining in older adults and monitor for anticholinergic toxicity in others. Reduce the dose or stop one agent if symptoms develop.
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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