Testosterone supplementation is the introduction of exogenous testosterone into the human body. The process has become more and more common over the years, both as an illegal tool for athletes and bodybuilders and as a medical treatment for aging men whose natural testosterone levels have declined and patients of any age suffering from hypogonadism, or decreased function of the sex glands. Testosterone supplementation can have numerous effects, both physical and psychological.
Some of the primary effects of testosterone supplementation are anabolic, which means that they promote cell growth. These effects include the acceleration of amino acid to protein synthesis, improved appetite, increases in bone growth and density, acceleration of the production of red blood cells in bone marrow, and acceleration of the formation of muscle fibers and growth of skeletal muscle. Because of these effects on muscular development and strength, testosterone supplementation is often employed by athletes and bodybuilders in an attempt to gain an unnatural advantage.
Androgenic effects, also known as virilizing effects, refer to the processes by which supplemental testosterone causes the formation of masculine characteristics. Examples of this include growth of the penis in pubescent and prepubescent males; enlargement of the clitoris in women; growth of facial hair, pubic hair and other body hairs; deepening of the voice; and increased sex drive.
Adverse Physical Effects
Because testosterone supplementation is exogenous and unnatural, it can have adverse physical effects on recipients. The influx of exogenous testosterone suppresses processes of the testes, including natural testosterone production and sperm production, and compels the male body to produce excess estrogen, leading to the development of gynecomastia, a condition in which the male's breast tissue enlarges. Supplementation can also have a negative effect on cardiovascular health, including high blood pressure, elevated cholesterol, and cardiovascular or coronary artery disease, especially in those with pre-existing tendencies toward these conditions. In children and adolescents, testosterone supplementation can cause the premature fusion of growth plates, stunting growth.
Adverse Psychological Effects
Testosterone supplementation has been hypothesized as a causal factor in both aggressive and depressive behavior. Studies have come to divergent conclusions over whether or not testosterone-induced aggression, often called roid rage, is a real phenomenon. A 2006 study following two pairs of identical twins found "high levels of aggressiveness, hostility, anxiety and paranoid ideation in the twins who used [supplemental testosterone]." Studies on the link between supplemental testosterone and depression have been inconclusive, finding that supplementation could both cause and treat depressive symptoms depending on the circumstances.