Testosterone is responsible for the normal growth and development of the male sex organs and for the maintenance of the secondary sexual characteristics. The drug can affect the growth of the prostate, testis, seminal vesicles, penis and scrotum and also is important for body growth. Even though testosterone is an androgenic hormone, it does posses anabolic properties. Its use has been shown to promote protein synthesis and a positive nitrogen balance in the presence of a rich calorie diet.
Testosterone also has the ability to cause a mild increase in the production of red blood cells by stimulating the synthesis of EPO from the kidney. This results in an increase in the red blood cells and hence an increase in the oxygen carrying capacity.
When testosterone is taken for prolonged periods, it inhibits the release of Gonadotropins from the pituitary gland through a negative feedback mechanism. At large doses, it can even inhibit spermatogenesis.