Rifampin and Tamoxifen interaction
Rifampin 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 Rifampin (Rifadin IV) label · effective 2026-05-27
…Antiarrhythmics Disopyramide Decrease exposure Mexiletine Decrease exposure Quinidine Decrease exposure Propafenone Decrease AUC by 50%–67% Tocainide Decrease exposure Antiestrogens Tamoxifen Decrease AUC by 86% Toremifene Decrease steady state concentrations of toremifene in serum Antithrombotic Agents Clopidogrel Prevention or Management: Concomitant use of clopidogrel…
From the Tamoxifen (SOLTAMOX) label · effective 2021-11-29
Inducers of CYP3A4 Strong CYP3A4 inducers should not be used with tamoxifen.
Strong CYP3A4 inducers (e.g., rifampin) reduce tamoxifen AUC and C max [see Clinical Pharmacology (12.3) ] .
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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.