Nebido injection contains the active ingredient testosterone undecanoate, which is an ester of the naturally occurring male hormone testosterone.
Testosterone is known as an androgen. It is produced by the testicles and is the main hormone essential for normal growth and development of the male sex organs and male sexual characteristics.
The natural production of testosterone is controlled by another set of hormones called gonadotrophins, which are released from the pituitary gland in the brain.
During adult life, testosterone is essential for the production of sperm, the maintenance of sex drive, erectile potency, and the functioning of the prostate gland and other reproductive structures. It also has functions in the skin, muscles, skeleton, kidney, liver, bone marrow and central nervous system.
Low levels of testosterone can cause decreased sex drive, impotence, infertility due to decreased sperm production, decreased mental and physical activity, fatigue and weakening of bones (osteoporosis). Testosterone is given as replacement therapy when natural testosterone levels fall too low, causing problems such as those above.
Natural testosterone levels fall slowly with age and fall rapidly following surgical removal of the testicles (for example in the treatment of testicular cancer). They may also fall due to decreased functioning of the testicles (hypogonadism or eunuchoidism) caused by testicular disease, or by decreased gonadotrophin production by the pituitary gland, as a result of pituitary disease.
Testosterone replacement allows natural testosterone levels to return to normal, thus relieving the symptoms of the deficiency.