Testosterone is a steroid hormone from the androgen group. Although it is the main male sex hormone, it plays key roles in both males and females such as enhancing libido, energy, and immune function, and protecting against osteoporosis. On average, an adult male's body produces about twenty times the amount of testosterone that an adult female's body does.
For men around the age of 40, testosterone begins to drop. For women, it drops after age 50. This is accompanied by a decrease in libido and difficulty in erectile function.
Anabolic steroids such as testosterone have been taken to enhance muscle development, strength, and/or endurance. After a series of scandals and publicity in the 1980s (such as Ben Johnson's improved performance at the 1988 Summer Olympics), prohibitions of anabolic steroid use were renewed or strengthened by many sports organizations, and it was made a "controlled substance" by the United States Congress.
Replacement therapy can take the form of injectables (such as testosterone cypionate or testosterone enanthate in oil), transdermal patches, creams and gels, subcutaneous pellets and oral therapy. At the time of writing, new delivery methods are being developed, including a "roll on" and a nasal spray.
As a prescription, it is available as a patch, a pill, under the tongue and as an injection. For women, testosterone in a smaller dose is usually added to the estrogen (Estratest) or in a combination with estrogen and progesterone by a compounding pharmacy.
Testosterone's effects include anabolic effects such as growth of muscle mass and strength (testosterone is an anabolic steroid), increased bone density and strength, and stimulation of linear growth and bone maturation; and virilizing effects such as maturation of the sex organs, particularly the penis and the formation of the scrotum in fetuses, and after birth (usually at puberty) a deepening of the voice, growth of the beard and axillary hair.
As with every hormone, testosterone has been tried for many conditions and purposes besides replacement, with variable success. 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.
Not only does the testosterone cause improvement of hot flashes, but it increases general well being and libido, induces weight loss if obese and helps in preventing and treating osteoporosis.
Some doctors have noted that since the advent of Viagra, men have stopped asking for repeat prescriptions of testosterone. This may indicate that their main concern was taking the hormone for increased sexual function.
Some doctors test testosterone levels and, if less than 800 for men, consider prescribing this very important hormone.
Testosterone use involves relatively high rates of side-effects or problems.
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. This hormone replacement therapy helps to maintain serum testosterone levels in the normal range.
Testosterone levels decline gradually with age in men. The clinical significance of this decrease is debatable, and there is no general agreement regarding if and when to treat aging men with testosterone replacement therapy. The position of the American Society of Andrology is that testosterone therapy "is indicated when both clinical symptoms and signs suggestive of androgen deficiency and decreased testosterone levels are present". Unfortunately, the signs and symptoms are non-specific, and are generally associated with aging such as loss of muscle mass and bone density, decreased physical endurance, decreased memory ability and loss of libido.
Testosterone causes suppression of spermatogenesis and can lead to infertility.
Low testosterone levels are frequently the reason for diminished interest in sex, both in men and in women.
More serious complications arising from testosterone supplementation include exacerbation of sleep apnea.
Testosterone supplementation causes the acceleration of pre-existing prostate cancer growth. It is recommended that physicians screen for prostate cancer with a digital rectal exam and PSA (prostate specific antigen) level prior to initiating therapy, and monitor hematocrit and PSA levels closely during therapy.
The popular image of this sex hormone is primarily as a muscle-building machismo-inducing substance that "pumps men up", yet clinical research is uncovering important roles for testosterone in many other diverse areas of health and physiology, including the brain. New evidence suggests that testosterone may enhance memory function and protect against the development of Alzheimer's disease.
Neuroscientists from Rockefeller University and Weill Medical College of Cornell University recently discovered that when neural cells from the brains of rats are exposed to testosterone, the cells don't produce as much Amyloid beta-peptide (AB-peptide). The accumulation of AB-peptide can cause plaque deposits to form in the brain. These deposits are believed to play a major role in the development of Alzheimer's disease.
Testosterone in addition appears to improve certain cognitive abilities in men, such as verbal and spatial memory function. Levels of bioavailable testosterone are especially important, researchers emphasized, because these levels decline most rapidly as men and women age.
Since high levels of testosterone have been linked with prostate cancer in men and endometriosis in women, however, they urged caution when using replacement therapy, carefully weighing the risks and benefits for each patient.
Increasing levels of adrenal hormones such as cortisol, which rise in response to stress and aging, may also play an important role in Alzheimer's. High levels of these hormones can damage the hippocampus region in the brain, causing
learning impairment and memory loss. Testosterone, however, shows the potential to reverse some of this damage.
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