Femara (Steroids) basic info. Femara Anti-Estrogen Powder Letrozole Alias: Letrozole CAS NO.: 112809-51-5 Molecular Formula: C17H11N5 Molecular Weight: 285.31 White or light yellow crystal Method of Analysis: HPLC Standard: USP/BP Femara Description: Femara lowers estrogen levels in postmenopausal women, which may slow the growth of certain types of breast tumors that need estrogen to grow in the body. Femara is …