Letrozole and Letrozole Interaction
Drug interaction information between Letrozole and Letrozole.
Letrozole and Letrozole have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Letrozole and Letrozole. 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
Cimetidine does not have a meaningful effect on how letrozole is processed or used by the body.
FDA Label Information
7 DRUG INTERACTIONS Tamoxifen Coadministration of Femara and tamoxifen 20 mg daily resulted in a reduction of letrozole plasma levels of 38% on average (Study P015). Clinical experience in the second-line breast cancer trials (AR/BC2 and AR/BC3) indicates that the therapeutic effect of Femara therapy is not impaired if Femara is administered immediately after tamoxifen. Cimetidine A pharmacokinetic interaction study with cimetidine (Study P004) showed no clinically significant effect on letrozole pharmacokinetics.
Letrozole Also Interacts With
- Warfarin minor
- Cimetidine minor
- Tamoxifen minor
Letrozole Also Interacts With
- Tamoxifen moderate
- Warfarin minor
- Cimetidine minor
Frequently Asked Questions
What SPL severity band is on file for Letrozole (Fertility) + Letrozole?
Compiled FDA labeling labels this pair minor. That is a source-record field, not an individual medication-combination decision.
How many labeled pairs sit in each drug's minor band?
Letrozole and Letrozole tie at 4 labeled pairs each. minor-band counts: Letrozole 4 alongside Warfarin, Cimetidine, Tamoxifen; Letrozole 3 alongside Warfarin, Cimetidine.
What mechanism field is on file for Letrozole (Fertility) and Letrozole?
Cimetidine does not have a meaningful effect on how letrozole is processed or used by the body.
Letrozole and Letrozole · minor-band peers
SPL source-record counts only. This page's band is minor · classes on file: Letrozole (Aromatase Inhibitor (Off-Label Fertility)); Letrozole (Aromatase Inhibitor).
0 major · 0 moderate · 4 minor · 4 total
- Other minor peers for Letrozole
- Warfarin
- Cimetidine
- Tamoxifen
0 major · 1 moderate · 3 minor · 4 total
- Other minor peers for Letrozole
- Warfarin
- Cimetidine
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.