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).
In men, low testosterone levels in the body can be supplemented by hormone replacement with testosterone. Testosterone replacement therapy can be prescribed as an intramuscular injection usually given on a biweekly basis; as a patch or gel placed on the skin, or as putty that is applied to the gums of the mouth. Each of the treatments has its risks and benefits. The decision as to which form of testosterone to use depends upon the clinical situation. Discussions between the patient and health care professional often helps decide which medication to use.
In the United States there are currently no preparations that are FDA approved for testosterone replacement for women.