Mifepristone and misoprostol are the two medicines used in a medical abortion. Mifepristone is the first pill taken and works as an anti-progesterone to block the effects of progesterone, a hormone needed to sustain a pregnancy. Misoprostol is taken later and contains prostaglandins that cause cramping and bleeding to empty the uterus. Together this combination of mifepristone and misoprostol is over 90% effective in ending a pregnancy within the first nine weeks.