Letrozole is an orally active, nonsteroidal, selective aromatase inhibitor and hence an antiestrogen which may prevent the formation of estrogens, and therefore reduce or prevent the unwanted and feminizing effects that include male breast development (gynecomastia), water retention, and belly fat. It prevents aromatase from producing estrogens by competitive, reversible binding to the heme of its cytochrome P450 unit. The action is specific, and letrozole does not reduce production of corticosteroids. Letrozole inhibits the liver enzyme CYP2A6, and to a lesser extent CYP2C19, in vitro, but no relevant interactions with drugs like cimetidine and warfarin have been observed.
Molar Mass: 285.303 g/mol