Low-dose mifepristone for contraception: a weekly versus planned postcoital randomized pilot study.

In this randomized pilot study, we compared the contraceptive efficacy, safety and side effect profiles of weekly versus planned postcoital regimens of low-dose mifepristone. Forty participants were randomized to receive mifepristone 10 mg weekly or planned postcoitally (to be used no more frequently than once every 5 days), for 12 consecutive months. Participants were evaluated monthly to determine pregnancy, ovulation status and acceptability of physical side effects. We ended this pilot study prematurely due to low efficacy and predetermined stopping rules. Three pregnancies during 56 woman-months occurred in the weekly group and three pregnancies during 68 woman-months occurred in the planned postcoital group. Almost half of the participants ovulated monthly on either regimen. The majority of the participants found the physical side effects of these regimens acceptable. Participants in the planned postcoital group, however, found adhering to the regimen more difficult than those in the weekly group. Mifepristone 10 mg used weekly or planned postcoitally did not adequately prevent pregnancy in our pilot study population. Although the concept of intermittent low-dose mifepristone is appealing, the contraceptive effectiveness was disappointing.