Testosterone cypionate (Depo-Testosterone), testosterone enanthate (Xyosted, available generically), testosterone undecanoate (Aveed), and testosterone pellet (Testopel) are forms of testosterone injection used to treat symptoms of low testosterone in men who have hypogonadism (a condition in which the body does not produce enough natural testosterone). Testosterone is used only for men with low testosterone levels caused by certain medical conditions, including disorders of the testicles, pituitary gland (a small gland in the brain), or hypothalamus (a part of the brain) that cause hypogonadism. Your doctor will order certain lab tests to check your testosterone levels to see if they are low before you begin to use testosterone injection. Testosterone enanthate (available generically) and testosterone pellet (Testopel) are also used to stimulate puberty in males with delayed puberty. Testosterone enanthate (available generically) injection may be used in certain women with a type of breast cancer called mammary cancer that has spread to other parts of the body. Testosterone should not be used to treat the symptoms of low testosterone in men who have low testosterone due to aging ('age related hypogonadism'). Testosterone is in a class of medications called androgenic hormones. Testosterone is a hormone produced by the body that contributes to the growth, development, and functioning of the male sexual organs and typical male characteristics. Testosterone injection works by supplying synthetic testosterone to replace the testosterone that is normally produced naturally in the body. When used to treat breast cancer, testosterone works by stopping the release of estrogen.