Drug interactions
Olanzapine + Promethazine
Severity: Moderate
Olanzapine 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
Both drugs block dopamine receptors and are sedating and anticholinergic, so combining them increases sedation, orthostatic hypotension and the risk of extrapyramidal symptoms. There is also additive QT and anticholinergic burden.
What this interaction means in plain words
Olanzapine 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.
Olanzapine belongs to Central Nervous System; Promethazine belongs to Respiratory.
Why it happens
Additive dopamine D2, histamine H1 and muscarinic receptor antagonism.
What to do
Monitor sedation, blood pressure and movement disorders, and consider ECG in patients with QT risk factors. Avoid routine co-prescription in older patients.
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 Olanzapine
Frequently asked questions
Can I take Olanzapine with Promethazine?
MediHelp rates the interaction as moderate. Olanzapine 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. Both drugs block dopamine receptors and are sedating and anticholinergic, so combining them increases sedation, orthostatic hypotension and the risk of extrapyramidal symptoms. There is also additive QT and anticholinergic burden.
How serious is the interaction between Olanzapine 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: Monitor sedation, blood pressure and movement disorders, and consider ECG in patients with QT risk factors. Avoid routine co-prescription in older patients.
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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