Drug interactions
Promethazine + Thiothixene
Severity: Moderate
Promethazine and Thiothixene: 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 cause sedation, so combined use may increase extrapyramidal symptoms, drowsiness and anticholinergic effects. The risk of neuroleptic malignant syndrome and QT prolongation may also be additive.
What this interaction means in plain words
Promethazine and Thiothixene 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.
Why it happens
Additive dopamine D2 antagonism, CNS depression and anticholinergic activity.
What to do
Monitor for movement disorders, excessive sedation, fever or rigidity, and consider an ECG if other QT-prolonging drugs 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
Frequently asked questions
Can I take Promethazine with Thiothixene?
MediHelp rates the interaction as moderate. Promethazine and Thiothixene 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 cause sedation, so combined use may increase extrapyramidal symptoms, drowsiness and anticholinergic effects. The risk of neuroleptic malignant syndrome and QT prolongation may also be additive.
How serious is the interaction between Promethazine and Thiothixene?
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 movement disorders, excessive sedation, fever or rigidity, and consider an ECG if other QT-prolonging drugs 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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