RU 486 (or Mifepristone) is a steroid hormone resembling progesterone. Developed in France in 1980 by Dr. Etienne-Emile Baulieu for Roussel-Uclaf, RU 486 is the first antiprogestin, a breakthrough in birth control technology. The name RU 486 comes from Roussel-Uclaf's initials and an arbitary lab serial number. It is also commonly called the abortion pill.
RU 486, in conjunction with a prostaglandin, is 95.5% effective in terminating pregnancy during the first 7 weeks. Up to eight weeks it is more reliable than surgical abortion.