Drug interactions
Promethazine + Risperidone
Severity: Moderate
Promethazine and Risperidone: 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
Both drugs have dopamine-blocking and sedating properties, so the combination raises the risk of extrapyramidal symptoms, excessive sedation and hypotension. Both can prolong the QT interval, adding to the risk of arrhythmia.
What this interaction means in plain words
Promethazine and Risperidone 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 belongs to Respiratory; Risperidone belongs to Central Nervous System.
Why it happens
Additive dopamine D2 and histamine H1 antagonism, with additive QT prolongation; promethazine may also inhibit CYP2D6 weakly.
What to do
Monitor for sedation, extrapyramidal signs and orthostatic hypotension, and check an ECG and electrolytes in patients with QT risk factors. Use the lowest effective doses and limit duration.
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
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Other interactions of Risperidone
- Ibutilide + Risperidone Contraindicated
- Risperidone + Vandetanib Contraindicated
- Adagrasib + Risperidone Major
- Amiodarone + Risperidone Major
- Amisulpride + Risperidone Major
- Amoxapine + Risperidone Major
Frequently asked questions
Can I take Promethazine with Risperidone?
MediHelp rates the interaction as moderate. Promethazine and Risperidone 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. Both drugs have dopamine-blocking and sedating properties, so the combination raises the risk of extrapyramidal symptoms, excessive sedation and hypotension. Both can prolong the QT interval, adding to the risk of arrhythmia.
How serious is the interaction between Promethazine and Risperidone?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for sedation, extrapyramidal signs and orthostatic hypotension, and check an ECG and electrolytes in patients with QT risk factors. Use the lowest effective doses and limit duration.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Ibutilide, Pimozide, Thioridazine. The full list is on the Promethazine page.
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