CYP2D6 and breast cancer: Furthermore, aforementioned antidepressant drugs used in conjunction with tamoxifen could affect anticancer efficacy of endocrine therapy and increase the risk of recurrence of breast cancer due to inhibition of cytochrome P450 2D6 (CYP2D6) and by reducing the active metabolite of tamoxifen-endoxifen plasma concentrations [23–25].