Drug interactions
Promethazine + Thioridazine
Severity: Contraindicated
Promethazine and Thioridazine: contraindicated 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
Thioridazine strongly prolongs the QT interval and is associated with torsades de pointes, and promethazine adds further risk along with sedative and anticholinergic effects. Thioridazine labeling warns against co-use with other QT-prolonging drugs.
What this interaction means in plain words
Promethazine and Thioridazine are not normally used together. Taking them at the same time is expected to cause harm or make one of them unsafe, so a different medicine is usually chosen for one of the two.
Promethazine belongs to Respiratory; Thioridazine belongs to Central Nervous System.
Why it happens
Additive QT prolongation, with thioridazine being a high-risk agent, plus additive CNS depression.
What to do
Do not combine; use a non-QT-prolonging alternative to promethazine.
What to ask your pharmacist
- Is there an alternative to one of these two medicines for me?
- If both are essential, who is monitoring me and how often?
- Which symptoms mean I should stop and seek help straight away?
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Other interactions of Promethazine
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
- Belladonna and opium + Promethazine Major
Other interactions of Thioridazine
- Abiraterone + Thioridazine Contraindicated
- Adagrasib + Thioridazine Contraindicated
- Amiodarone + Thioridazine Contraindicated
- Amisulpride + Thioridazine Contraindicated
- Amitriptyline + Thioridazine Contraindicated
- Amoxapine + Thioridazine Contraindicated
Frequently asked questions
Can I take Promethazine with Thioridazine?
MediHelp rates the interaction as contraindicated. Promethazine and Thioridazine are not normally used together. Taking them at the same time is expected to cause harm or make one of them unsafe, so a different medicine is usually chosen for one of the two. Thioridazine strongly prolongs the QT interval and is associated with torsades de pointes, and promethazine adds further risk along with sedative and anticholinergic effects. Thioridazine labeling warns against co-use with other QT-prolonging drugs.
How serious is the interaction between Promethazine and Thioridazine?
MediHelp rates it contraindicated, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Do not combine; use a non-QT-prolonging alternative to promethazine.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Ibutilide, Pimozide, Alfentanil. The full list is on the Promethazine page.
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