Drug interactions
Haloperidol + Promethazine
Severity: Major
Haloperidol and Promethazine: major 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 can prolong the QT interval, and haloperidol carries a recognized risk of torsades de pointes, particularly with intravenous use or high doses. They also add to sedation and anticholinergic effects.
What this interaction means in plain words
Haloperidol and Promethazine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Haloperidol belongs to Central Nervous System; Promethazine belongs to Respiratory.
Why it happens
Additive blockade of cardiac potassium (hERG) channels causing QT prolongation, plus additive CNS depression.
What to do
Avoid when possible; if both are required, check baseline and follow-up ECG, correct potassium and magnesium, and limit doses.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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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 Haloperidol
- Dofetilide + Haloperidol Contraindicated
- Dronedarone + Haloperidol Contraindicated
- Haloperidol + Ibutilide Contraindicated
- Haloperidol + Levoketoconazole Contraindicated
- Haloperidol + Panobinostat Contraindicated
- Haloperidol + Pimozide Contraindicated
Frequently asked questions
Can I take Haloperidol with Promethazine?
MediHelp rates the interaction as major. Haloperidol and Promethazine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Both drugs can prolong the QT interval, and haloperidol carries a recognized risk of torsades de pointes, particularly with intravenous use or high doses. They also add to sedation and anticholinergic effects.
How serious is the interaction between Haloperidol and Promethazine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid when possible; if both are required, check baseline and follow-up ECG, correct potassium and magnesium, and limit 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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