Drug interactions
Belladonna and opium + Diphenhydramine
Severity: Major
Belladonna and opium and Diphenhydramine: major 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
This combination adds anticholinergic effects from belladonna and diphenhydramine to opioid-related CNS and respiratory depression. It can cause marked sedation, urinary retention, constipation or ileus, and respiratory depression.
What this interaction means in plain words
Belladonna and opium and Diphenhydramine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Additive antimuscarinic effects and additive CNS and respiratory depression via H1 blockade and opioid receptor agonism.
What to do
Avoid combining if possible; otherwise use the lowest doses and monitor sedation, respiratory rate and bowel and bladder function. Take particular care in older or debilitated patients.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Belladonna and opium and Diphenhydramine, 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 14 days on the web. No card needed.
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Belladonna and opium with Diphenhydramine?
MediHelp rates the interaction as major. Belladonna and opium and Diphenhydramine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. This combination adds anticholinergic effects from belladonna and diphenhydramine to opioid-related CNS and respiratory depression. It can cause marked sedation, urinary retention, constipation or ileus, and respiratory depression.
How serious is the interaction between Belladonna and opium and Diphenhydramine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid combining if possible; otherwise use the lowest doses and monitor sedation, respiratory rate and bowel and bladder function. Take particular care in older or debilitated patients.
What other medicines interact with Diphenhydramine?
MediHelp also lists interactions of Diphenhydramine with, for example, Alfentanil, Benzhydrocodone / acetaminophen, Brexanolone. 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.
