Drug interactions
Diamorphine + Promethazine
Severity: Major
Diamorphine and Promethazine: 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
Promethazine and diamorphine (heroin) both depress the central nervous system, so together they can cause marked sedation, hypotension and respiratory depression. Promethazine is sometimes used with opioids for antiemetic effect, but the sedative burden is increased.
What this interaction means in plain words
Diamorphine and Promethazine 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 CNS and respiratory depression through H1 antagonism and opioid receptor agonism.
What to do
Start with reduced doses and monitor sedation and respiratory rate closely, particularly in opioid-naive, elderly or respiratory-compromised 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?
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References
Other interactions of Promethazine
- Cabergoline + Promethazine Contraindicated
- Dopamine + Promethazine Contraindicated
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
Frequently asked questions
Can I take Diamorphine with Promethazine?
MediHelp rates the interaction as major. Diamorphine and Promethazine 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. Promethazine and diamorphine (heroin) both depress the central nervous system, so together they can cause marked sedation, hypotension and respiratory depression. Promethazine is sometimes used with opioids for antiemetic effect, but the sedative burden is increased.
How serious is the interaction between Diamorphine and Promethazine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Start with reduced doses and monitor sedation and respiratory rate closely, particularly in opioid-naive, elderly or respiratory-compromised patients.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Cabergoline, Dopamine, Ibutilide. The full list is on the Promethazine page.
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