Testosterone is a steroid hormone produced in the adrenal glands of both sexes and in the testes of males and the ovaries of females. Testosterone is largely responsible for the formation and maintenance of male sex characteristics, including both the larger bone and muscle development seen in males. The testosterone levels in humans are regulated by hormones released from the brain; in males the hypothalamus and pituitary glands in the brain increase testosterone during puberty and male characteristics develop (for example, penile enlargement, facial hair, interest in sex).
While the adrenal glands still help out with testosterone and progesterone production in later years, the amount supplied is extremely small. The biggest issue that we see is an end to normal estrogen levels when the body converts excess testosterone into estradiol. This causes an imbalance that leads to a condition called estrogen dominance – where estrogen is now unopposed by progesterone and testosterone because their levels have declined. Estrogen dominance leads to weight gain, which further increases testosterone to estrogen conversion.