Mifepristone blocks the action of progesterone, a hormone necessary to sustain pregnancy.
Mifepristone is used in combination with a prostaglandin called misoprostol. Mifepristone has already been successfully used by over 200,000 women worldwide as a method of early abortion, and may be a possible treatment for fibroid tumors, ovarian cancer, endometriosis, meningioma, and some types of breast cancer. Methotrexate , also used in combination with misopristol, terminates a pregnancy by inhibiting the production of folic acid. Methotrexate is currently the only method of medical abortion that effectively terminates ectopic pregnancy. The Campaign for RU 486 and Contraceptive Research is a project of the Feminist Majority Foundation that fought to bring this method of early abortion and possible terminal disease treatment to the United States.