Low-T, or low-testosterone, is either a lack of production or underproduction of the testosterone hormone in men and women. In males, testosterone is produced primarily in the testicles and is responsible for sexual function and male development. Testosterone is also responsible for the building of bone mass and muscles, as well as sperm production and sex drive, or libido, in men. Testosterone can influence other body processes such as red blood cell production, bone density, and male pattern fat distribution. As men over 30 start to age, their testosterone levels naturally decline. Testosterone levels peak in early adulthood for normally developing males, with the decline after that being part of the normal aging process. However, in cases of low T, testosterone production is unnaturally low. This can be the result of a chronic medical condition such as medications, obesity, diabetes, infections, liver or kidney disease, or other conditions related to the body’s hormones. Low-T can cause low libido, infertility, sexual dysfunction, change in sleep patterns, weight gain, decreased strength, and emotional changes.