This medication is used in men who do not make enough of a natural substance called testosterone. In males, testosterone is responsible for many normal functions, including the growth and development of the genitals, muscles, and bones. It also helps cause normal sexual development (puberty) in boys. Methyltestosterone is similar to the natural testosterone produced by your body. It belongs to a class of drugs known as androgens. It works by affecting many body systems so that the body can develop and function normally. Methyltestosterone may also be used in certain adolescent boys to cause puberty in those with delayed puberty. It may also be used to treat certain types of breast cancer in women.