Testosterone is the principal male sex hormone. Although testosterone does also occur in women, (produced in the ovaries and adrenal glands), testosterone levels in women are only about a tenth of those in men.

In men, testosterone is produced in the testes and adrenal glands. It is the chief player in bringing about sexual development in the male. Andropause (male equivalent of the menopause) is finally gaining wide attention around the world, as demonstrated by the concern raised at the Second World Congress on the Aging Male in Geneva, February 2000, where the World Health Organization described male health as a "neglected" area of modern medicine.

Dr. Richard Bebb of Vancouver, Canada reported some of the striking benefits of testosterone therapy for bone density of the spines in androgen deficient males. Dr. Alvaro Palacios from Venezuela reported oral testosterone undecanoate was effective in treating men with PADAM (symptoms of physical, vasomotor, psychological and sexual problems in aging men). London cardiologist, Dr. Peter Collins, states: "it seems that testosterone acts as an anti-ischemic drug in men with coronary heart disease and decreased levels of plasma testosterone."

It is known that there are more testosterone receptors in the heart muscle than in other muscles of the human. As is the case for most of the other hormones, the levels of testosterone diminish as a man ages with the levels of free testosterone (biologically active) dropping by 2% per year after the age of 30 years. With the decline of testosterone levels, there is generally an accompanying decline in other aspects of a man's health that are associated with testosterone. Not many years ago, testosterone was feared by the public as a bad hormone, causing aggression and symptoms of maleness. It was even a triplicate prescription in some areas of Canada under the same control category as Demerol and Morphine.