Tamoxifen API (Active Pharmaceutical Ingredient) is the pure, bulk powder form of the drug Tamoxifen Citrate, a key selective estrogen receptor modulator (SERM) used mainly to treat and prevent hormone-receptor-positive breast cancers, working as an anti-estrogen by blocking estrogen's effects on cancer cells. INN / Common name: Tamoxifen citrate CAS No.: 54965-24-1 Molecular formula: C₂₈H₃₂N₂O·C₆H₈O₇ (citrate salt) Molecular weight: ~563.64 g/mol Breast cancer treatment For estrogen receptor–positive (ER+) breast cancer in pre- and postmenopausal women. Used in adjuvant therapy (after surgery) or treatment of metastatic disease. Breast cancer prevention In high-risk women, tamoxifen reduces the risk of developing breast cancer. Other estrogen-related conditions (off-label, limited) Certain gynecomastia cases in men Fertility treatments (rare off-label use in women to induce ovulation) Mechanism of action (brief) Tamoxifen blocks estrogen receptors in breast tissue, preventing estrogen from promoting tumor growth. In other tissues (bone, uterus), it may act as a partial agonist, producing estrogen-like effects. Identification IR spectroscopy: Conforms to reference spectrum UV / HPLC: Retention time matches certified reference standard Melting point: Within reference range (~140–144 °C for citrate salt) Assay (Potency) Typically 98.0–102.0% (on anhydrous basis)