Mifepristone, also known as RU-486, is a medication typically used with misoprostol to bring about anabortion. This combination is more than 95% effective during the first 50 days of pregnancy. It is also effective in the second trimester of pregnancy. Two weeks after use effectiveness should be verified. It is taken by mouth. 
Common side effects include abdominal pain, feeling tired, and vaginal bleeding. Serious side effects may include heavy vaginal bleeding, bacterial infection, and a malformed baby if the pregnancy does not end. If used, appropriate follow up care needs to be available. Mifepristone works by blocking the effects ofprogesterone and causing contractions of the uterus.