CYP2D6 and breast cancer: SSRIs and, in particular, fluoxetine and paroxetine as the strongest CYP2D6 inhibitors, may therefore prevent the formation of the active metabolite from inactive tamoxifen (Crewe et al. 1997; Desta et al. 2004) and put breast cancer patients under anti-oestrogenic treatment at an increased risk of breast cancer recurrence (Singh et al. 2011).