Drug interactions
Cimetidine + Diazepam
Severity: Moderate
Cimetidine and Diazepam: 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
Cimetidine slows the hepatic metabolism of diazepam and its active metabolite desmethyldiazepam, prolonging half-life and increasing sedation and psychomotor impairment. The effect is greater in older patients and those with liver disease.
What this interaction means in plain words
Cimetidine and Diazepam 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.
Cimetidine belongs to Gastrointestinal Tract; Diazepam belongs to Musculoskeletal.
Why it happens
Cimetidine inhibits CYP2C19 and CYP3A4, decreasing diazepam N-demethylation and hydroxylation.
What to do
Monitor for excess sedation and consider reducing the diazepam dose, or switch to a benzodiazepine cleared by glucuronidation such as lorazepam. Alternatively use ranitidine-free alternatives such as famotidine.
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 Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram Major
Other interactions of Diazepam
Frequently asked questions
Can I take Cimetidine with Diazepam?
MediHelp rates the interaction as moderate. Cimetidine and Diazepam 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. Cimetidine slows the hepatic metabolism of diazepam and its active metabolite desmethyldiazepam, prolonging half-life and increasing sedation and psychomotor impairment. The effect is greater in older patients and those with liver disease.
How serious is the interaction between Cimetidine and Diazepam?
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 excess sedation and consider reducing the diazepam dose, or switch to a benzodiazepine cleared by glucuronidation such as lorazepam. Alternatively use ranitidine-free alternatives such as famotidine.
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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