Androgen, term embracing any of the male sex hormones, substances that induce and maintain secondary sex characteristics in males. The principal androgen is testosterone, produced in the testes of males and in the adrenal glands of both sexes. Testosterone circulates in the blood and is excreted in the urine. Androgens function principally, beginning at puberty, in the stimulation of such male secondary sex characteristics as development of the genital organs and maturation of sperm, growth of body hair, and changes in the larynx that lower the voice. Androgens have an anabolic effect—that is, they stimulate protein synthesis and inhibit protein breakdown, enhancing the growth of muscle and bone tissue in the developing male. An excess of androgens can lead to a variety of disorders, including the accentuation of male secondary sex characteristics in both males and females. Less frequently, an excess of androgens may cause testicular or ovarian tumors. For a discussion of the related female sex hormones, see Estrogen.