The principal sex hormone in males, testosterone plays a major role in sexual development and health in both sexes. Men produce about 20 times as much testosterone as women. Conversely, women produce a greater level of estrogen, which is the principal female sex hormone.

Testosterone promotes muscle growth, bone mass stability and body hair growth. It can also affect the libido (sex drive). As men get older, they naturally produce less testosterone; women begin to produce more testosterone during menopause.