The abortion pill is very effective. When misoprostol and mifepristone are used together, they have about a 98 percentTrusted Source effectiveness rate. The age of the pregnancy, the medication doses and administration, and whether or not a woman has been pregnant before may impact the effectiveness. The effectiveness rate decreases for each additional week of pregnancy.
While this effectiveness rate is high, it’s possible for a medical abortion to fail to terminate a pregnancy. In these cases, a woman would need to then undergo a surgical abortion.