– (E/Z)-Droloxifene is a mixture comprising (E)-Droloxifene, known as a selective estrogen receptor modulator, and (Z)-Droloxifene. (E)-Droloxifene binds to estrogen receptors (ER) in rabbit uterine homogenate with an IC50 of 24 nM. It increases uterine weight in immature rats and reduces the uterine weight increase caused by estradiol in juvenile rats. Additionally, (E)-Droloxifene inhibits the growth of human breast cancer cells MCF-7, ZR-75-1, and T47D stimulated by 17β-estradiol. In contrast, (Z)-Droloxifene shows weak binding to ER and exhibits neither estrogenic nor anti-estrogenic activity.