Drug interactions
Promethazine + Quetiapine
Severity: Moderate
Promethazine and Quetiapine: 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 block dopamine and histamine receptors, so combining them increases sedation, orthostatic hypotension and the risk of extrapyramidal symptoms. Both also have some potential to prolong the QT interval.
What this interaction means in plain words
Promethazine and Quetiapine 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; Quetiapine belongs to Central Nervous System.
Why it happens
Additive antidopaminergic, antihistaminic and CNS-depressant effects, with possible additive QT prolongation.
What to do
Monitor for oversedation, hypotension and movement disorders, and obtain an ECG if other QT-prolonging drugs or electrolyte disturbances are present. Use the lowest effective doses.
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 Quetiapine
- Adagrasib + Quetiapine Major
- Amiodarone + Quetiapine Major
- Amisulpride + Quetiapine Major
- Amoxapine + Quetiapine Major
- Anagrelide + Quetiapine Major
- Apalutamide + Quetiapine Major
Frequently asked questions
Can I take Promethazine with Quetiapine?
MediHelp rates the interaction as moderate. Promethazine and Quetiapine 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 block dopamine and histamine receptors, so combining them increases sedation, orthostatic hypotension and the risk of extrapyramidal symptoms. Both also have some potential to prolong the QT interval.
How serious is the interaction between Promethazine and Quetiapine?
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 oversedation, hypotension and movement disorders, and obtain an ECG if other QT-prolonging drugs or electrolyte disturbances are present. Use the lowest effective doses.
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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