Tamoxifen is a selective estrogen receptor modulator (SERM) that acts as an ER agonist in the endometrium and as an ER antagonist in breast tissue; it also inhibits PKC. Tamoxifen exhibits anticancer chemotherapeutic, anti-angiogenic, anti-osteoporotic, and antipsychotic activities. Tamoxifen is also a prodrug, transformed into the active metabolite 4-hydroxytamoxifen in vivo. Tamoxifen shows some benefit in clinical settings in the treatment of bipolar I disorder and other mood disorders. In animal models, tamoxifen decreases blood vessel formation and inhibits angiogenesis. In osteoclasts, this compound induces apoptosis by increasing expression of FasL. Additionally, tamoxifen acts as a functional inhibitor of acid sphingomyelinase (FIASMA).