WHO special programme of research, development and research training in human reproduction. Task force on long-acting agents for the regulation of fertility.

A multicentre phase III clinical trial has been undertaken to compare norethisterone enantate (NET-EN) given by two different treatment regimens and depot-medroxyprogesterone acetate (DMPA). After 18 months of observation, preliminary findings are reported for 1,589 women who received DMPA 150mg every 90 days; 790 women who received NET-EN 200mg every 60 days; and 796 women who received NET-EN, 200mg every 60 days for 6 months, then 200mg every 84 days. The overall discontinuation rates per 100 women were similar for all three treatment groups over the 18 months observation (61.8 - 63.5 per 100 women). The discontinuation rates for bleeding problems and for personal reasons were also similar for all three treatment groups. However, terminations due to amenorrhoea were significantly higher among DMPA users (12.1 and 17.4 per 100 women at 12 and 18 months) as compared with both NET-EN groups (6.8 - 8.2 per 100 women at 12 months and 10.4 - 10.9 per 100 women at 18 months). The only significant difference in pregnancy rates observed between the three groups was a higher rate at 18 months among NET-EN (84 days) users (1.6 per 100 women), as compared with DMPA users (0.2 per 100 women). There was no overall significant difference between the two NET-EN groups, although between the 6 and 18 month's follow-up when the two NET-EN regimens diverged, the NET-EN (84 days) users' pregnancy rate rose significantly, whereas in the NET-EN (60 days) group the pregnancy rate did not change. There was a significantly higher weight gain in those subjects using NET-EN at 60-day intervals compared with those using it at 84-day intervals.