Tamoxifen and Anastrozole Interaction
Drug interaction information between Tamoxifen and Anastrozole.
Tamoxifen and Anastrozole have a documented major interaction in FDA labeling.
FDA drug labeling documents a major-severity interaction between Tamoxifen and Anastrozole. 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 Tamoxifen + Anastrozole?
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: Tamoxifen has 2 (also Warfarin); Anastrozole has 1.
What mechanism field is on file for Tamoxifen and Anastrozole?
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: Tamoxifen (Selective Estrogen Receptor Modulator (SERM)); Anastrozole (Aromatase Inhibitor).
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.