Drug interactions
Cimetidine + Warfarin
Severity: Moderate
Cimetidine and Warfarin: 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 can increase warfarin anticoagulant effect and raise the INR. This increases the risk of bleeding, particularly in the first weeks of combined therapy.
What this interaction means in plain words
Cimetidine and Warfarin 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; Warfarin belongs to Cardiovascular.
Why it happens
Cimetidine inhibits CYP enzymes (notably CYP1A2 and CYP3A4, and CYP2C19) that metabolize the R-enantiomer of warfarin, reducing its clearance.
What to do
Check the INR more frequently when starting, stopping or changing cimetidine, and adjust the warfarin dose accordingly. Consider famotidine or a proton pump inhibitor instead.
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 Warfarin
- Defibrotide + Warfarin Contraindicated
- Ketorolac + Warfarin Contraindicated
- Abciximab + Warfarin Major
- Acetylsalicylic acid + Warfarin Major
- Adagrasib + Warfarin Major
- Amiodarone + Warfarin Major
Frequently asked questions
Can I take Cimetidine with Warfarin?
MediHelp rates the interaction as moderate. Cimetidine and Warfarin 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 can increase warfarin anticoagulant effect and raise the INR. This increases the risk of bleeding, particularly in the first weeks of combined therapy.
How serious is the interaction between Cimetidine and Warfarin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check the INR more frequently when starting, stopping or changing cimetidine, and adjust the warfarin dose accordingly. Consider famotidine or a proton pump inhibitor instead.
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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