Drug interactions
Diphenhydramine + Promazine
Severity: Moderate
Diphenhydramine and Promazine: 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 sedating and strongly anticholinergic, so combined use can cause additive drowsiness, confusion, urinary retention, constipation and dry mouth. Diphenhydramine also inhibits CYP2D6, which may modestly raise promazine exposure.
What this interaction means in plain words
Diphenhydramine and Promazine 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 anticholinergic and CNS depressant effects, plus CYP2D6 inhibition by diphenhydramine reducing promazine metabolism.
What to do
Monitor for sedation and anticholinergic effects, especially in older adults, and reduce the dose of either drug if these occur. Avoid the combination in patients with delirium risk or 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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Diphenhydramine and Promazine, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Promazine?
MediHelp rates the interaction as moderate. Diphenhydramine and Promazine 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 sedating and strongly anticholinergic, so combined use can cause additive drowsiness, confusion, urinary retention, constipation and dry mouth. Diphenhydramine also inhibits CYP2D6, which may modestly raise promazine exposure.
How serious is the interaction between Diphenhydramine and Promazine?
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 sedation and anticholinergic effects, especially in older adults, and reduce the dose of either drug if these occur. Avoid the combination in patients with delirium risk or urinary retention.
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.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
