Ospemifene-d 4 is a deuterium labeled Ospemifene. Ospemifene is a selective and orally active estrogen receptor modulator for the prevention of osteoporosis with IC50 values of 827 nM and 1633 nM for estrogen receptor α ( ERα ) and ERβ , respectively. Ospemifene has bone-sparing, antitumor, and cholesterol-lowering effects.