Testosterone undecanoate (Nebido) is authorized for testosterone replacement therapy of primary and secondary male hypogonadism, i.e., if testosterone deficiency has been confirmed both by clinical and by laboratory tests. Testosterone undecanoate provides testosterone to men whose testes do not produce enough testosterone. The injection is an intramuscularly administered depot preparation of Testosterone undecanoate. Following intramuscular injection of Testosterone undecanoate as an oily solution, the com-pound is gradually released from the depot and immediately cleaved by serum esterases into testosterone and undecanoic acid.