Warfarin and Tamoxifen Interaction
Drug interaction information between Warfarin and Tamoxifen.
Warfarin and Tamoxifen have a documented major interaction in FDA labeling.
FDA drug labeling documents a major-severity interaction between Warfarin and Tamoxifen. This page displays the available source-record category and label text. The category is not an individual risk estimate or medication-combination direction.
How They Interact
Tamoxifen increases the blood-thinning effects of warfarin, which can lead to a much higher risk of dangerous bleeding.
FDA Label Information
( 7.1 ) Warfarin: Do not use in patients taking tamoxifen for DCIS and for reduction in breast cancer incidence in women at high risk. Warfarin A marked increase in anticoagulant effect may occur when tamoxifen is used in combination with warfarin. Closely monitor coagulation indices in patients who are taking tamoxifen for either the treatment of metastatic breast cancer or as adjuvant therapy who require concomitant use of warfarin [see Contraindications (4) ] .
Warfarin Also Interacts With
- Fluoxetine major
- Ibuprofen moderate
- Aspirin moderate
- Diclofenac moderate
- Desvenlafaxine moderate
Tamoxifen Also Interacts With
- Anastrozole major
- Letrozole moderate
- Bupropion minor
- Desvenlafaxine minor
- Letrozole (Fertility) minor
Frequently Asked Questions
What SPL severity band is on file for Warfarin + Tamoxifen?
Compiled FDA labeling labels this pair major. That is a source-record field, not an individual medication-combination decision.
Which drug in this pair has the larger labeled-interaction portfolio?
Warfarin has 163 labeled pairs on file vs Tamoxifen's 10. In the major band specifically: Warfarin has 2 (also Fluoxetine); Tamoxifen has 2 (also Anastrozole).
What mechanism field is on file for Warfarin and Tamoxifen?
Tamoxifen increases the blood-thinning effects of warfarin, which can lead to a much higher risk of dangerous bleeding.
Warfarin's labeled portfolio outnumbers Tamoxifen
SPL source-record counts only. This page's band is major · classes on file: Warfarin (Vitamin K Antagonist (Anticoagulant)); Tamoxifen (Selective Estrogen Receptor Modulator (SERM)).
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. This registry does not provide individual medication-combination directions.
Read our methodology - how this data is sourced, computed, and verified.