Tamoxifen and Warfarin: Drug Interaction Guide

Quick answer: This is a major interaction — avoid combining Tamoxifen and Warfarin unless specifically directed by your doctor.

Interaction severity: Major — avoid combination

How Tamoxifen interacts with Warfarin

Tamoxifen inhibits CYP2C9-mediated metabolism of S-warfarin, potentiating its anticoagulant effect and raising bleeding risk.

What you should do

Avoid the combination in patients on warfarin for non-essential indications; otherwise reduce warfarin dose and monitor INR weekly until stable.

Key facts

Severity

Major — avoid combination

Mechanism

Tamoxifen inhibits CYP2C9-mediated metabolism of S-warfarin, potentiating its anticoagulant effect and raising bleeding ...

Action

Avoid the combination in patients on warfarin for non-essential indications; otherwise reduce warfarin dose and monitor ...

Important medical disclaimer: This page provides educational information about drug interactions for general reference. It is not a substitute for professional medical advice, diagnosis, or treatment. Always discuss your specific medications with a qualified healthcare provider before starting, stopping, or changing any treatment. About our editorial team.

Frequently asked questions

Can I take Tamoxifen and Warfarin together?

No — this combination should generally be avoided. Avoid the combination in patients on warfarin for non-essential indications; otherwise reduce warfarin dose and monitor INR weekly until stable.

What is the severity of this interaction?

The interaction between Tamoxifen and Warfarin is classified as Major — avoid combination. Tamoxifen inhibits CYP2C9-mediated metabolism of S-warfarin, potentiating its anticoagulant effect and raising bleeding risk.

What should I do if I'm prescribed both?

Avoid the combination in patients on warfarin for non-essential indications; otherwise reduce warfarin dose and monitor INR weekly until stable. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

Last reviewed: by iMedic Medical Editorial Team. Our editorial process.