Testosterone is a steroid hormone belonging to the androstane class and is the primary sex hormone and androgen in males. While primarily known as a male hormone, females also produce testosterone in smaller amounts. In men, it is mainly produced in the testicles, and in women, in the ovaries and adrenal glands. This hormone plays a key role in the development of male reproductive tissues like the testes and prostate, and it promotes secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair. Testosterone is also associated with sex drive, aggression, and behavior. In both sexes, it impacts overall mood, cognition, cardiovascular health, bone density, and energy levels.
Testosterone levels naturally fluctuate throughout life, increasing significantly during puberty and then gradually declining with age, about 1% to 2% each year after early adulthood. In males, normal testosterone levels range from 265 to 923 nanograms per deciliter (ng/dL), while females have much lower levels, typically between 15 to 70 ng/dL. Low testosterone can lead to reduced muscle mass, fatigue, depression, and sexual dysfunction. Testosterone replacement therapy (TRT) is used to treat low testosterone levels (hypogonadism) and may improve bone strength and reduce fracture risk. However, TRT carries potential risks, including acne, sleep apnea, and increased red blood cell count. Some studies suggest it may increase the risk of heart disease and prostate cancer, though this is still debated.
