No male hormonal contraceptive is ready for clinical use. Most trials were small exploratory studies. Their power to detect important differences was limited and their results imprecise. In addition, assessment of azoospermia can vary by sensitivity of the method used. Future trials need more attention to the methodological requirements for RCTs. More trials with adequate power would also be helpful.
Levonorgestrel implants enhanced the suppression of spermatogenesis by testosterone implants: comparison between Chinese and non-Chinese men.
Previous male contraceptive studies showed that progestins enhance spermatogenesis suppression by androgens in men.
                We compared the efficacy of spermatogenesis suppression by the combination of levonorgestrel (LNG) with testosterone (T) implants to that by T implants alone in two different ethnic groups.
                This was a randomized trial performed in two centers with two treatment groups.
                The study was performed at the Academic Medical Center in the United States and the Research Institute in China.
                Forty non-Chinese and 40 Chinese healthy male volunteers were studied.
                Subjects were randomized to receive four LNG implants together with four T implants (inserted on d 1 and wk 15-18) vs. T implants alone for 30 wk.
                The primary end point compared the efficiency of suppression to severe oligozoospermia (1 x 10(6)/ml) by LNG plus T implants vs. that by T implants alone. The secondary end point examined differences in spermatogenesis suppression between Chinese and non-Chinese subjects.
                LNG plus T implants caused more suppression of spermatogenesis to severe oligozoospermia during the treatment period than T implants alone at both sites (P < 0.02). In Chinese men, severe oligozoospermia was achieved in more than 90% of the men in both treatment groups. Suppression to severe oligozoospermia was less in the non-Chinese men (59%) after T alone (P < 0.020); this difference disappeared with combined treatment (89%). T implant extrusion occurred in six men. Acne and increased hemoglobin were the most common adverse events.
                T implants resulted in more pronounced spermatogenesis suppression in Chinese men. Addition of LNG implants to T implants enhanced the suppression of spermatogenesis in the treatment period in both Chinese and non-Chinese men.