Objective: The study investigated the contraceptive effect of weekly administration of mifepristone.
Subjects and methods: A double-blind, randomized clinical trial with weekly doses of 25 or 50 mg of mifepristone was carried out in three centers in China. Women were assigned to either of two groups. We defined each study cycle as 28 days. All bleeding data were derived from women's menstrual cards. The outcome measures were contraceptive efficacy, changes of menstrual pattern and side effects.
Results: Eighty-three women were enrolled and the outcome was known in 76 women: 39 in the 25-mg group and 37 in the 50-mg group. No pregnancy occurred in both groups in 456 women-months of use accumulated. There were no significant differences in mean bleeding days and no bleeding days between the two groups in the first three study cycles. In the fourth, fifth and sixth cycles, mean bleeding days in the 50-mg group (0.86, 1.05 and 0.62, respectively) were significantly less than those in the 25-mg group (3.5, 2.87 and 2.4 respectively); mean no bleeding days in the 50-mg group (26.07, 25.95 and 26.11, respectively) were significantly more than those in the 25-mg group (22.93, 23.23 and 23.51, respectively), and the percentage of women who had no bleeding in a 28-day study cycle in the 50-mg group (22.3%, 25% and 21.1%, respectively) was significantly more than those in the 25-mg group (2.6%, 3.9% and 3.9%, respectively). Side effects, such as nausea and breast distension, were uncommon and mild.
Conclusion: Once weekly administration with 25-mg mifepristone is a potentially effective method for regular contraception.