Tamoxifen relies on CYP2D6 to generate the active metabolite endoxifen; potent CYP2D6-inhibiting antidepressants such as paroxetine can depress endoxifen concentrations by up to 72%, an interaction linked to increased breast-cancer mortality when exposure overlap exceeds 6 months (Hansten, 2018). Here, CYP2D6 is linked to breast cancer.