Drug interactions
Chlorpromazine + Methadone
Severity: Major
Chlorpromazine and Methadone: major interaction.
Last updated Sources: US FDA label
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, raising the risk of torsades de pointes, and both cause sedation, which may lead to additive CNS and respiratory depression and hypotension. The risk is higher with electrolyte abnormalities, heart disease or high doses.
What this interaction means in plain words
Chlorpromazine and Methadone 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.
Chlorpromazine belongs to Central Nervous System; Methadone belongs to Musculoskeletal.
Why it happens
Additive QT prolongation through cardiac potassium channel blockade, plus additive CNS depression.
What to do
Obtain a baseline ECG and monitor the QTc after starting or changing doses, and correct potassium and magnesium. Consider an alternative antipsychotic with less QT effect and monitor sedation.
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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References
Other interactions of Methadone
- Alvimopan + Methadone Contraindicated
- Calcium / magnesium / potassium / sodium oxybates + Methadone Contraindicated
- Droperidol + Methadone Contraindicated
- Ibutilide + Methadone Contraindicated
- Isocarboxazid + Methadone Contraindicated
- Lefamulin + Methadone Contraindicated
Other interactions of Chlorpromazine
- Chlorpromazine + Dofetilide Contraindicated
- Chlorpromazine + Dronedarone Contraindicated
- Chlorpromazine + Droperidol Contraindicated
- Chlorpromazine + Ibutilide Contraindicated
- Chlorpromazine + Metrizamide Contraindicated
- Chlorpromazine + Panobinostat Contraindicated
Frequently asked questions
Can I take Chlorpromazine with Methadone?
MediHelp rates the interaction as major. Chlorpromazine and Methadone 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, raising the risk of torsades de pointes, and both cause sedation, which may lead to additive CNS and respiratory depression and hypotension. The risk is higher with electrolyte abnormalities, heart disease or high doses.
How serious is the interaction between Chlorpromazine and Methadone?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Obtain a baseline ECG and monitor the QTc after starting or changing doses, and correct potassium and magnesium. Consider an alternative antipsychotic with less QT effect and monitor sedation.
What other medicines interact with Methadone?
MediHelp also lists interactions of Methadone with, for example, Alvimopan, Calcium / magnesium / potassium / sodium oxybates, Droperidol. The full list is on the Methadone page.
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