Anastrozole and Tamoxifen Interaction
Drug interaction information between Anastrozole and Tamoxifen.
Anastrozole and Tamoxifen have a documented major interaction in FDA labeling.
FDA drug labeling documents a major-severity interaction between Anastrozole 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 lowers the amount of anastrozole in your blood, which may make the treatment less effective against cancer. Research also shows that taking both drugs together provides no extra benefit compared to taking just one.
FDA Label Information
7 DRUG INTERACTIONS Tamoxifen: Do not use in combination with anastrozole. No additional benefit seen over tamoxifen monotherapy ( 7.1 , 14.1 ). 7.1 Tamoxifen Co-administration of anastrozole and tamoxifen in breast cancer patients reduced anastrozole plasma concentration by 27%.
Tamoxifen Also Interacts With
- Warfarin major
- Letrozole moderate
- Bupropion minor
- Desvenlafaxine minor
- Letrozole (Fertility) minor
Frequently Asked Questions
What SPL severity band is on file for Anastrozole + 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?
Tamoxifen has 10 labeled pairs on file vs Anastrozole's 2. In the major band specifically: Anastrozole has 1; Tamoxifen has 2 (also Warfarin).
What mechanism field is on file for Anastrozole and Tamoxifen?
Tamoxifen lowers the amount of anastrozole in your blood, which may make the treatment less effective against cancer. Research also shows that taking both drugs together provides no extra benefit compared to taking just one.
Tamoxifen carries more major-labeled pairs than Anastrozole
SPL source-record counts only. This page's band is major · classes on file: Anastrozole (Aromatase Inhibitor); Tamoxifen (Selective Estrogen Receptor Modulator (SERM)).
Tamoxifen has 2 major-labeled pairs vs Anastrozole's 1.
1 major · 0 moderate · 1 minor · 2 total
Anastrozole has no other major-band peer in this dataset besides Tamoxifen.
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.