Tamoxifen Citrate is an orally active selective estrogen receptor modulator (SERM) that blocks estrogen activity in breast cells while activating estrogen signaling in cells such as those of the bone, liver, and uterus. As an Hsp90 activator, it enhances the ATPase activity of the Hsp90 chaperone complex, induces autophagy and apoptosis, and can be used to generate gene knockout models in CreER(T2) transgenic mice as well as liver injury models.