Comparison of three single doses of mifepristone as emergency contraception: a randomised trial

Background Mifepristone is a highly effective and well-tolerated emergency contraceptive when given in a dose of 660 mg within 72 h of unprotected coi tus. We assessed whether the same effectiveness can be achieved with lower doses of mifepristone (50 mg and 10 mg) and a longer postcoital treatment p eriod (120 h). Methods We undertook a multicentre, single-masked, randomised trial in 11 f amily-planning clinics in Australia, China, Finland, Georgia, the UK, and t he USA. 1717 healthy women with regular menstrual cycles who requested emer gency contraception within 120 h of unprotected coitus were randomly assign ed to three treatment groups. Findings 32 women were lost to follow-up and one was pregnant before treatm ent. The 600 mg, 50 mg, and 10 mg groups did not differ in the proportions of pregnancies (seven [1.3%] of 559, six [1.1%] of 560, and seven [1.2%] of 565). Two pregnancies (both in the 50 mg group) were tubal. Among women wi thout further acts of intercourse, treatment delay did not appear to influe nce the effectiveness. No major side-effects occurred, except a delay in th e onset of next menses, significantly (p<0.01) related to the mifepristone dose. Interpretation Lowering the dose of mifepristone sixty-fold did not decreas e its effectiveness as an emergency contraceptive under typical use, though a study of this size cannot exclude differences in effectiveness up to alm ost three-fold. Lower doses of mifepristone were associated with less distu rbance of the menstrual cycle. Thus, a dose as low as 10 mg seems preferabl e to the 600 mg dose.