Testosterone is the primary sex steroid hormone in males. Testosterone is in charge of the male’s reproductive organ development, including the testes and prostate, and promotes secondary sexual characteristics. The primary sites of testosterone production are the testicles in males and the ovaries in females. The precursor of testosterone is cholesterol. The half-life of the hormone: 2–4 hours and turns into inactive substances in the liver. The content of testosterone in the blood of a healthy young man is about 630 ng/dl, the normal rates ranging from 264 to 916 ng/dl. In men, testosterone levels drop at a rate of 1-2% per year with age.