Letro 2.5 mg is a medication used to treat breast cancer in post-menopausal women. It a type of aromatase inhibitor, which works by preventing the production of estrogen in the body. Each tablet contains 2.5 milligrams of letrozole, and a package comes with 100 tablets. Letrozole can help slow the growth of some breast cancer cells that rely on estrogen to grow. It is typically taken once a day, with or without food.