Herb-Drug Interactions with Tamoxifen in Breast Cancer Patients: A Systematic Review

Abstract

Introduction: Tamoxifen is a cornerstone of endocrine therapy for ER-positive breast cancer. Its metabolism via CYP2D6 can be altered by co-administered substances, including herbal supplements, potentially compromising its efficacy. This review synthesizes the evidence on herb-tamoxifen interactions.

Methods: A systematic review of pharmacokinetic studies, case reports, and preclinical studies was conducted across several databases. The focus was on interactions between commonly used herbs (e.g., St. John's Wort, Black Cohosh, Curcumin) and tamoxifen or its active metabolite, endoxifen.

Results: The evidence showed strong inhibition of CYP2D6 by certain herbs, which could theoretically reduce the conversion of tamoxifen to endoxifen, thereby lowering its efficacy. However, direct clinical evidence from outcome studies is scarce. In contrast, some herbs like curcumin showed potential for synergistic effects without significant pharmacokinetic interaction.

Discussion: The potential for clinically significant herb-tamoxifen interactions is high, but currently under-investigated in patient outcome studies. Oncologists and patients should exercise caution when combining herbal supplements with endocrine therapy.

Conclusion: Caution is warranted when using herbal supplements with tamoxifen due to the potential for adverse pharmacokinetic interactions.