Scientists long have sought to use androgens—either alone or in combination with other drugs— as a male contraceptive. Because the high concentration of testosterone within the testes, approximately one hundred times that in the peripheral circulation, is necessary for spermatogenesis, suppression of endogenous testosterone production greatly diminishes spermatogenesis. Initial use of testosterone alone required supraphysiologic doses, while addition of GnRH agonists required daily injections. An alternative approach is to combine a progestin with a physiological dose of testosterone to attempt to suppress LH secretion and spermatogenesis but provide a normal serum testosterone concentration; clinical trials are ongoing.
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