Rates of testosterone-induced suppression to severe oligozoospermia or azoospermia in two multinational clinical studies. World Health Organization Task force on Methods for The Regulations of Male Fertility.

Two multicentre studies of the contraceptive efficacy of azoospermia and severe oligozoospermia were conducted in 16 centres in 10 countries. They used a common protocol of weekly testosterone injections for sperm suppression, the patterns and degrees of which were compared among men from different population groups. Six hundred and seventy normal, health volunteers, of whom 205 were Asian (mostly Chinese) and 465 of non-Asian origin, were given weekly injections of testosterone enanthate, 200 mg IM, during the suppression (6-month) and efficacy (12-month) phases. Patterns of sperm suppression were assessed by semen analysis at monthly or 2-weekly intervals. Sperm counts suppressed more slowly in the Asian than in the non-Asian men in the first 2 months of injections but subsequently suppressed to lower sperm concentrations below 5 million/ml, 3 million/ml or azoospermia at 6 months were 97.1% 95.6%, and 66.7%, respectively for non-Asian men, compared to 99.4%, 98.4% and 89.2%, respectively for Asian men. In conclusion, a hormonal contraceptive method based on regular testosterone injections can suppress spermatogenesis to azoospermia or severe oligozoospermia in 97% of men, regardless of their ethnic origin.