Drug interactions
Diazepam + Promethazine
Severity: Moderate
Diazepam and Promethazine: 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
Promethazine and diazepam both depress the central nervous system, and their combination can cause marked sedation, impaired coordination and respiratory depression. The risk is higher in older patients, those with lung disease, and when alcohol or opioids are also taken.
What this interaction means in plain words
Diazepam and Promethazine 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.
Diazepam belongs to Musculoskeletal; Promethazine belongs to Respiratory.
Why it happens
Additive CNS depression from H1 antagonism and GABA-A positive modulation.
What to do
Use the lowest effective doses and monitor sedation and respiratory function, especially after the first doses. Advise against driving and alcohol.
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?
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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 Diazepam
Frequently asked questions
Can I take Diazepam with Promethazine?
MediHelp rates the interaction as moderate. Diazepam and Promethazine 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. Promethazine and diazepam both depress the central nervous system, and their combination can cause marked sedation, impaired coordination and respiratory depression. The risk is higher in older patients, those with lung disease, and when alcohol or opioids are also taken.
How serious is the interaction between Diazepam and Promethazine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use the lowest effective doses and monitor sedation and respiratory function, especially after the first doses. Advise against driving and alcohol.
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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