RU-486, also known as Mifepristone, was invented in 1980 by Dr. Etienne-Emile Baulieu for the French pharmaceutical company Roussel-Uclaf. Because it is a competitive inhibitor of progesterone, it is classified as one of several new birth control drugs called 'antiprogestins'

RU-486 is a steroid hormone similar in the structure to the natural hormone progesterone. This structure enables it to competitively bind to the progesterone binding site. RU-486 can be used for the termination of an early pregnancy (first nine weeks). Therefore, it is also known as the 'abortion pill' or the 'morning after pill'. Other uses for this drug include treatment for fibroid fumors, ovarian cancer, endometriosis, meningioma, and some types of breast cancer.