Dubbed the "French abortion pill" and the "month after pill", the pharmaceutical RU-486 hit the European scene like gangbusters in 1988, but was delayed for licensing in the United States by the Food and Drug Administration because of political pressure against abortions until September 2000. In France, where the drug was developed, about one third of all abortions are performed with the synthetic steroidal hormone.

View a second image of mifepristone.

Known to doctors as mifepristone and to pharmacists by the trade name mifeprex, RU-486 is a synthetic prostaglandin that interferes with progesterone metabolism. By making the uterine lining inhospitable to the developing embryo, the zygote fails to attach, is deprived of nutrients, and is miscarried. As a three-pill prescription, mifepristone is first ingested and followed two days later by two misoprostol tablets, which causes contractions and expulsion of its contents. Methotrexate stops embryonic cells from dividing, ending the pregnancy and can be combined with the other drugs. As an at-home option and alternative to surgery, RU-486 provides a private procedure for terminating first trimester pregnancy. It can also function as a "morning-after pill" and as a menstrual initiator.

Originally named RU 486 by the French pharmaceutical company Roussel-Uclaf (thus "RU"), mifepristone features 29 carbons, 35 hydrogens, 1 nitrogen and 2 oxygen atoms per molecule in contrast to a molecule of the natural hormone progesterone with 21 carbons, 30 hydrogens, and 2 oxygen atoms. RU-486 acts as an antagonist for progesterone by binding to the progesterone site, and tying itself to the hormone and also blocking its release. Mifepristone is a substituted 19-nor steroid compound designated by organic chemists as 11-beta-[p-(dimethylamino)phenyl]-17beta-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one. It forms a yellow powder with a molecular weight of 429.6, a melting point of 191 to 196 degrees Celsius, and is insoluble in water or hexane and very soluble in methanol, chloroform, or acetone.

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