Drug interactions
Morphine + Promethazine
Severity: Major
Morphine 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 adds to the central nervous system and respiratory depressant effects of morphine. This can cause profound sedation, hypotension and respiratory depression, particularly in opioid-naive, elderly or frail patients.
What this interaction means in plain words
Morphine 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.
Morphine belongs to Musculoskeletal; Promethazine belongs to Respiratory.
Why it happens
Additive CNS and respiratory depression from phenothiazine antihistamine and opioid agonist activity.
What to do
Start with reduced doses of one or both drugs and monitor sedation level and respiratory rate. Avoid in patients with respiratory compromise when possible.
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
Other interactions of Morphine
- Alvimopan + Morphine Contraindicated
- Isocarboxazid + Morphine Contraindicated
- Morphine + Olanzapine / samidorphan Contraindicated
- Morphine + Phenelzine Contraindicated
- Morphine + Tranylcypromine Contraindicated
- Alfentanil + Morphine Major
Frequently asked questions
Can I take Morphine with Promethazine?
MediHelp rates the interaction as major. Morphine 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 adds to the central nervous system and respiratory depressant effects of morphine. This can cause profound sedation, hypotension and respiratory depression, particularly in opioid-naive, elderly or frail patients.
How serious is the interaction between Morphine 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 of one or both drugs and monitor sedation level and respiratory rate. Avoid in patients with respiratory compromise when possible.
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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