GNRH1 and Azoospermia: In a randomized clinical trial in 2004,different GnRH antagonist preparations were found to cause azoospermia in 39 of47 subjects, and more recently, acycline has been tested in contraceptivetrails, although its primary use is in the treatment of prostatecancer.71 Despite promising results, GnRH antagonists requiredaily or weekly injections, and incur high costs, leading to many drugdevelopers to not pursue them further (Table 1).