Spermatozoa are produced in the testes of males in a process called spermatogenesis. In order to render a man infertile, a hormone-based male contraceptive method must stop spermatogenesis by interrupting the release of gonadotropins from the pituitary gland. Even in low concentrations, trestolone is a potent inhibitor of the release of the gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH). In order for spermatogenesis to occur in the testes, both FSH and testosterone must be present. By inhibiting release of FSH, trestolone creates an endocrine environment in which conditions for spermatogenesis are not ideal. Manufacture of sperm is further impaired by the suppression of LH, which in turn drastically curtails the production of testosterone. Sufficient regular doses of trestolone cause severe oligozoospermia or azoospermia, and therefore infertility, in most men. Trestolone-induced infertility has been found to be quickly reversible upon discontinuation.