Natesto is a nasal gel used as hormone replacement therapy in adult males with a condition called hypogonadism, associated with a deficiency or absence of endogenous testosterone. Testosterone hormones are key to normal male growth and development of sex organs. Testosterone affects the growth and maturation of the prostate glands, seminal vesicles, penis, and scrotum. It is also responsible for the development and growth of male hair, such as facial, pubic, chest, and axillary hair. Other effects are the enlargement of laryngeal, thickening of vocal cords, body musculature, and fat distribution.