Drug interactions
Cimetidine + Clozapine
Severity: Major
Cimetidine and Clozapine: 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
Cimetidine can increase clozapine levels, with reports of increased sedation, seizures and other toxicity. Clozapine has a narrow therapeutic window, so exposure changes matter.
What this interaction means in plain words
Cimetidine and Clozapine 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.
Cimetidine belongs to Gastrointestinal Tract; Clozapine belongs to Central Nervous System.
Why it happens
Cimetidine inhibits CYP1A2 and CYP3A4 metabolism of clozapine.
What to do
Prefer famotidine or another acid suppressant; if cimetidine is used, monitor clozapine levels and for sedation, hypotension and seizures, and reduce the dose as required.
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 Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram Major
Other interactions of Clozapine
- Clozapine + Deferiprone Contraindicated
- Clozapine + Irinotecan Contraindicated
- Clozapine + Pimozide Contraindicated
- Clozapine + Thioridazine Contraindicated
- Acalabrutinib + Clozapine Major
- Adagrasib + Clozapine Major
Frequently asked questions
Can I take Cimetidine with Clozapine?
MediHelp rates the interaction as major. Cimetidine and Clozapine 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. Cimetidine can increase clozapine levels, with reports of increased sedation, seizures and other toxicity. Clozapine has a narrow therapeutic window, so exposure changes matter.
How serious is the interaction between Cimetidine and Clozapine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Prefer famotidine or another acid suppressant; if cimetidine is used, monitor clozapine levels and for sedation, hypotension and seizures, and reduce the dose as required.
What other medicines interact with Cimetidine?
MediHelp also lists interactions of Cimetidine with, for example, Dofetilide, Fezolinetant, Alfentanil. The full list is on the Cimetidine page.
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