Tamoxifen and Abiraterone: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Abiraterone
Tamoxifen
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased tamoxifen exposure, increased risk of tamoxifen-related adverse effects or reduced tamoxifen efficacy
Interaction Deep Dive
Abiraterone acetate is a moderate CYP2D6 inhibitor. Coadministration of with CYP2D6 substrates such as tamoxifen increases the concentration of CYP2D6 substrates, which may increase the risk of adverse reactions related to these substrates. Avoid coadministration for which minimal changes in concentration may lead to serious toxicities. If alternative treatments cannot be used, consider a dose reduction of the concomitant CYP2D6 substrate1. Coadministration of tamoxifen with a potent CYP2D6 inhibitor may inhibit the CYP2D6-mediated metabolism of tamoxifen to its active metabolite, endoxifen 2. Variations in endoxifen concentrations may result, which may reduce the antitumoral efficacy of tamoxifen and increase the risk of breast cancer relapse 4. A retrospective analysis revealed a 1.9-fold higher breast cancer recurrence rate in patients receiving a CYP2D6 inhibitor concomitantly with tamoxifen than in those who received tamoxifen alone 3.
Why it happens (mechanism)
Inhibition of CYP2D6-mediated tamoxifen metabolism by abiraterone acetate
Literature reports
3 reports — tap to read
a) The Cmax and AUC of dextromethorphan (CYP2D6 substrate) were increased 2.8- and 2.9-fold, respectively when dextromethorphan 30 mg was given with abiraterone acetate 1000 mg daily (plus prednisone). The AUC for dextrorphan, the active metabolite of dextromethorphan, increased approximately 1.3-fold 1.
b) A retrospective analysis of breast cancer patients revealed a 1.9-fold higher 2-year recurrence rate of breast cancer in patients receiving concomitant therapy with tamoxifen and a CYP2D6 inhibitor compared with those receiving tamoxifen therapy alone. Based on medical and pharmacy claims data, 1928 patients who were new to tamoxifen therapy in a 30-month period and who had follow-up data for at least 24 months were included in the analysis. Among these patients, 353 (median age, 53 years) received tamoxifen concurrently with a CYP2D6 inhibitor and 945 (median age, 52 years) received tamoxifen alone. Disease recurrence was identified by diagnosis and insurance billing codes for mastectomy, lumpectomy, lymph node dissection, or radiation therapy, occurring at least 6 months after initiation of tamoxifen therapy. The 2-year breast cancer recurrence rate was 13.9% in women receiving concomitant tamoxifen and CYP2D6 inhibitor therapy compared with 7.5% in women receiving tamoxifen alone (95% CI, 1.33 to 2.76, p=0.001; hazard ratio, 1.92). Intervention procedures in the tamoxifen/CYP2D6 inhibitor group to treat breast cancer included mastectomy (54%), lumpectomy (36%), and radiation therapy (47%); corresponding intervention rates in the tamoxifen only group were 52%, 38%, and 46%, respectively 3.
c) The use of CYP2D6 inhibitors should be avoided in breast cancer patients receiving tamoxifen due to the risk of substantially reduced plasma concentrations of the antiestrogenic tamoxifen metabolite, endoxifen. In a prospective randomized trial, 256 postmenopausal breast cancer patients receiving tamoxifen were genotyped and grouped according to CYP2D6 metabolism and medication history. Adjusted analysis showed that decreased metabolizers (n=65) had significantly worse relapse-free survival (hazard ratio 1.74; 95% confidence interval (CI), 1.1 to 2.74; p=0.017), disease-free survival (hazard ratio 1.6; 95% CI, 1.06 to 2.43; p=0.027), and shorter time to recurrence (hazard ratio 1.91; 95% CI, 1.05 to 3.45; p=0.034) compared with extensive metabolizers (n=115). The greatest risk of breast cancer relapse was found in the poor metabolizer group (hazard ratio 3.12; 95% CI, 1.37 to 7.55; p=0.007) 4. Decreased metabolizers had either one or two CYP2D6*4 alleles or was receiving a CYP2D6 inhibitor together with tamoxifen (regardless of genotype), and extensive metabolizers did not have a *4 allele and were not receiving a CYP2D6 inhibitor 5.
Common questions
Can I take Tamoxifen and Abiraterone together?
Increased tamoxifen exposure, increased risk of tamoxifen-related adverse effects or reduced tamoxifen efficacy Always confirm with your pharmacist or prescriber before making any change.
How serious is the Tamoxifen and Abiraterone interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Tamoxifen or Abiraterone need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (5)
- Product Information: AKEEGA(TM) oral tablets, niraparib, abiraterone acetate oral tablets. Janssen Biotech, Inc. (per FDA), Horsham, PA, 2023. DailyMed
- Johnson MD, Zuo H, Lee KH, et al: Pharmacological characterization of 4-hydroxy-N-desmethyl tamoxifen, a novel active metabolite of tamoxifen. Breast Cancer Res Treat 2004; 85(2):151-159. PubMed
- Aubert RE; Stanek EJ; and Yao J: Risk of breast cancer recurrence in women initiating tamoxifen with CYP2D6 inhibitors. American Society of Clinical Oncology. Alexandria, VA. 2009. DOI
- Goetz MP, Knox SK, Suman VJ, et al: The impact of cytochrome P450 2D6 metabolism in women receiving adjuvant tamoxifen. Breast Cancer Res Treat 2007; 101(1):113-121. PubMed
- Goetz MP, Kamal A, & Ames MM: Tamoxifen pharmacogenomics: the role of CYP2D6 as a predictor of drug response. Clin Pharmacol Ther 2008; 83(1):160-166. DOI
Keep reading about Abiraterone
Keep reading about Tamoxifen
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