Letrozole and Tamoxifen Interaction
Drug interaction information between Letrozole and Tamoxifen.
Letrozole and Tamoxifen have a documented moderate interaction in FDA labeling.
FDA drug labeling documents a moderate-severity interaction between Letrozole 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 letrozole in your blood, and it is not known if taking both together helps treat cancer effectively.
FDA Label Information
7 DRUG INTERACTIONS Anastrozole and letrozole: Should not be used in combination with tamoxifen. Letrozole The concomitant use of letrozole with tamoxifen is not recommended because the efficacy of the combination in the adjuvant treatment of breast cancer has not been established. Tamoxifen reduced the plasma concentration of letrozole by 38% when these drugs were co-administered [see Clinical Pharmacology (12.3) ].
Letrozole Also Interacts With
- Warfarin minor
- Cimetidine minor
- Letrozole (Fertility) minor
Tamoxifen Also Interacts With
- Warfarin major
- Anastrozole major
- Bupropion minor
- Desvenlafaxine minor
- Letrozole (Fertility) minor
Frequently Asked Questions
What SPL severity band is on file for Letrozole + Tamoxifen?
Compiled FDA labeling labels this pair moderate. 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 Letrozole's 4. In the moderate band specifically: Letrozole has 1; Tamoxifen has 1.
What mechanism field is on file for Letrozole and Tamoxifen?
Tamoxifen lowers the amount of letrozole in your blood, and it is not known if taking both together helps treat cancer effectively.
Tamoxifen carries more major-labeled pairs than Letrozole
SPL source-record counts only. This page's band is moderate · classes on file: Letrozole (Aromatase Inhibitor); Tamoxifen (Selective Estrogen Receptor Modulator (SERM)).
Tamoxifen has 2 major-labeled pairs vs Letrozole's 0. This page itself is in the moderate band, not the major band.
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.