pp replied: "Testosterone is a steroid hormone from the androgen group. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands. It is the principal male sex hormone and an anabolic steroid. In men, testosterone plays a key role in health and well-being as well as in sexual functioning. Examples include enhanced libido, increased energy, increased production of red blood cells and protection against osteoporosis. On average, an adult human male body produces about forty to sixty times more testosterone than an adult female body, but females are, from a behavioral perspective (rather than from an anatomical or biological perspective), more sensitive to the hormone.However the overall ranges for male and female are very wide, such that the ranges actually overlap at the low end and high end respectively.There are many routes of administration for testosterone. Forms of testosterone for human administration currently available include injectable (such as testosterone cypionate or testosterone enanthate in oil), oral, buccal,transdermal skin patches, and transdermal creams or gels. In the pipeline are "roll on" methods and nasal sprays.The original and primary use of testosterone is for the treatment of males who have too little or no natural endogenous testosterone production—males with hypogonadism. Appropriate use for this purpose is legitimate hormone replacement therapy (testosterone replacement therapy (TRT)), which maintains serum testosterone levels in the normal range. However, over the years, as with every hormone, testosterone or other anabolic steroids has also been given for many other conditions and purposes besides replacement, with variable success but higher rates of side effects or problems. Examples include infertility, lack of libido or erectile dysfunction, osteoporosis, penile enlargement, height growth, bone marrow stimulation and reversal of anemia, and even appetite stimulation. By the late 1940s testosterone was being touted as an anti-aging wonder drug (e.g., see Paul de Kruif's The Male Hormone). Decline of testosterone production with age has led to a demand for Androgen Replacement Therapy. To take advantage of its virilizing effects, testosterone is often administered to transmen as part of the hormone replacement therapy, with a "target level" of the normal male testosterone level. Like-wise, transwomen are sometimes prescribed anti-androgens to decrease the level of testosterone in the body and allow for the effects of estrogen to develop. Testosterone patches are effective at treating low libido in post-menopausal women. Low libido may also occur as a symptom or outcome of hormonal contraceptive use. Women may also use testosterone therapies to treat or prevent loss of bone density, muscle mass and to treat certain kinds of depression and low energy state. Women on testosterone therapies may experience an increase in weight without an increase in body fat due to changes in bone and muscle density. Most undesired effects of testosterone therapy in women may be controlled by hair-reduction strategies, acne prevention, etc. There is a theoretical risk that testosterone therapy may increase the risk of breast or gynaecological cancers, and further research is needed to define any such risks more clearly. There is a myth that exogenous testosterone can more or less definitively be used for male birth control. However, the vast majority of physicians will agree that to prescribe exogenous testosterone for this purpose is inappropriate. But, perhaps more"