Testosterone is the primary male sex hormone and androgen in males.[3] In humans, testosterone plays a key role in the development of male reproductive tissues such as testicles and prostate, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair. It is associated with increased aggression, sex drive, dominance, courtship display, and a wide range of behavioral characteristics.[4] In addition, testosterone in both sexes is involved in health and well-being, where it has a significant effect on overall mood, cognition, social and sexual behavior, metabolism and energy output, the cardiovascular system, and in the prevention of osteoporosis.[5][6] Insufficient levels of testosterone in men may lead to abnormalities including frailty, accumulation of adipose fat tissue within the body, anxiety and depression, sexual performance issues, and bone loss.
Testosterone is a steroid hormone from the androstane class containing a ketone and a hydroxyl group at positions three and seventeen respectively. It is biosynthesized in several steps from cholesterol and is converted in the liver to inactive metabolites.[8] It exerts its action through binding to and activation of the androgen receptor.[8] In humans and most other vertebrates, testosterone is secreted primarily by the testicles of males and, to a lesser extent, the ovaries of females. On average, in adult males, levels of testosterone are about seven to eight times as great as in adult females.[9] As the metabolism of testosterone in males is more pronounced, the daily production is about 20 times greater in men.[10][11] Females are also more sensitive to the hormone.[12][page needed]
^Tuck SP, Francis RM (2009). "Testosterone, bone and osteoporosis". Advances in the Management of Testosterone Deficiency. Frontiers of Hormone Research. Vol. 37. pp. 123–32. doi:10.1159/000176049. ISBN978-3-8055-8622-1. PMID19011293.
^Southren AL, Gordon GG, Tochimoto S, Pinzon G, Lane DR, Stypulkowski W (May 1967). "Mean plasma concentration, metabolic clearance and basal plasma production rates of testosterone in normal young men and women using a constant infusion procedure: effect of time of day and plasma concentration on the metabolic clearance rate of testosterone". The Journal of Clinical Endocrinology & Metabolism. 27 (5): 686–94. doi:10.1210/jcem-27-5-686. PMID6025472.
^Southren AL, Tochimoto S, Carmody NC, Isurugi K (November 1965). "Plasma production rates of testosterone in normal adult men and women and in patients with the syndrome of feminizing testes". The Journal of Clinical Endocrinology & Metabolism. 25 (11): 1441–50. doi:10.1210/jcem-25-11-1441. PMID5843701.
^"Testosterone". Drugs.com. American Society of Health-System Pharmacists. December 4, 2015. Archived from the original on August 20, 2016. Retrieved September 3, 2016.
^Liverman CT, Blazer DG, et al. (Institute of Medicine (US) Committee on Assessing the Need for Clinical Trials of Testosterone Replacement Therapy) (2004). "Introduction". Testosterone and Aging: Clinical Research Directions (Report). National Academies Press (US). Archived from the original on January 10, 2016. Retrieved September 26, 2016.