Mifepristone is a progesterone receptor blocker used in combination with misoprostol to terminate early pregnancies (up to 10 weeks gestation). By blocking progesterone, it causes the uterine lining to break down and the pregnancy to detach. Mifepristone is also used in some cases to treat fibroids or Cushing’s syndrome. It is typically administered in clinical settings as part of a medical abortion protocol.