It blocks the hormone progesterone to end pregnancy. This procedure causes the egg to detach from the womb lining.
For a better efficacy mifepristone should be used in association with a prostaglandin (misoprostol or gemeprost).
Mifepristone (RU-486) is a medical abortion medication with a long history of safety and effectiveness. First developed in the 1980’s in France, mifepristone blocks the hormone progesterone to end a pregnancy.
WHO’s recommended method for medical abortion, up to nine weeks of
amenorrhea, is mifepristone 200 mg, followed 24 to 48 hours by 800 mcg
For pregnancies of gestational age between 9 and 12 weeks (63–84 days) The recommended method for medical abortion is 200 mg mifepristone administered orally followed 36 to 48 hours later by 800 μg misoprostol administered vaginally. Subsequent misoprostol doses should be 400 μg, administered either vaginally or sublingually, every 3 hours up to four further doses, until expulsion of the products of conception. (Strength of recommendation: weak. Quality of evidence based on one randomized controlled trial and one observational study: low.)
The Royal College of Obstetricians and Gynecologists also recommends a treatment of 200 mg mifepristone followed by misoprostol
WHO has listed mifepristone in association with misoprostol as an essential drug for abortion up to nine weeks of amenohrea:
200 mg (1 tablet)