Drug interactions
Diamorphine + Diphenhydramine
Severity: Major
Diamorphine and Diphenhydramine: major interaction.
Last updated Sources: US FDA label
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
Diamorphine (heroin) is a potent opioid, and diphenhydramine is a sedating antihistamine. The combination increases sedation and can cause respiratory depression, coma and death, especially at high opioid doses. Older and opioid-naive patients are particularly at risk.
What this interaction means in plain words
Diamorphine 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 central nervous system and respiratory depression from opioid agonism and central H1 blockade.
What to do
Avoid concurrent use where possible and use the lowest effective doses when both are essential. Monitor sedation and respiratory rate closely.
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?
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References
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diamorphine with Diphenhydramine?
MediHelp rates the interaction as major. Diamorphine 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. Diamorphine (heroin) is a potent opioid, and diphenhydramine is a sedating antihistamine. The combination increases sedation and can cause respiratory depression, coma and death, especially at high opioid doses. Older and opioid-naive patients are particularly at risk.
How serious is the interaction between Diamorphine 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 concurrent use where possible and use the lowest effective doses when both are essential. Monitor sedation and respiratory rate closely.
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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