Anastrozole and Tamoxifen interaction
Anastrozole and Tamoxifen: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Anastrozole (ARIMIDEX) label · effective 2026-03-02
• Tamoxifen: Do not use in combination with ARIMIDEX.
Based on clinical and pharmacokinetic results from the ATAC trial, tamoxifen should not be administered with anastrozole.
• In women with pre-existing ischemic heart disease, an increased incidence of ischemic cardiovascular events occurred with ARIMIDEX use compared to tamoxifen use.
Ischemic Cardiovascular Events In women with pre-existing ischemic heart disease, an increased incidence of ischemic cardiovascular events was observed with ARIMIDEX in the ATAC trial (17% of patients on ARIMIDEX and 10% of patients on tamoxifen).
Patients receiving tamoxifen had a mean increase in both lumbar spine and total hip BMD compared to baseline.
From the Tamoxifen (SOLTAMOX) label · effective 2021-11-29
Anastrozole and letrozole: Should not be used in combination with tamoxifen.
In the ATAC trial, coadministration of anastrozole and tamoxifen in breast cancer patients reduced the anastrozole plasma concentration by 27% compared to that achieved with anastrozole alone.
Aromatase Inhibitors Anastrozole The combination of anastrozole and tamoxifen did not demonstrate any benefit when compared to tamoxifen alone and should be avoided in all patients [see Clinical Studies (14.2) ] .
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.