Mifepristone or RU-486 is an abortion pill used to terminate a pregnancy by blocking progesterone. It was developed in France in 1987 before being introduced to the United States in 2000 and Canada in January 2017. Mifepristone also softens the cervix making it easier to open and promotes contraction of the uterus when exposed to misoprostol.
In April 1980, as part of a formal research project at the French pharmaceutical company Roussel-Uclaf for the development of glucocorticoid receptor antagonists, chemist Georges Teutsch synthesized mifepristone (RU-38486, the 38,486th compound synthesized by Roussel-Uclaf from 1949 to 1980; shortened to RU-486)
The medical abortion pill mifepristone is most effective when used with either misoprostol or gemeprost. Mifepristone is a steroidal antiprogestogen, antiglucocorticoid and antiandrogen. In the presence of progesterone, mifepristone acts as a competitive progesterone receptor antagonist.
In the absence of progesterone, mifepristone acts as a partial agonist. Mifepristone is a 19-nor steroid with a bulky p-(dimethylamino) phenyl substituent above the plane of the molecule at the 11β-position responsible for inducing an inactive receptor conformation and a hydrophobic 1-propynyl substituent below the plane of the molecule at the 17α-position.
Mifepristone is also an antiglucocorticoid and a weak antiandrogen, its relative binding affinity at the progesterone receptor is more than twice that of progesterone, its relative binding affinity at the glucocorticoid receptor is more than three times that of dexamethasone and more than ten times that of cortisol;
During medical abortion mifepristone blockade of progesterone receptors directly causes endometrial decidual degeneration, cervical softening and dilatation, release of endogenous prostaglandins, and an increase in the sensitivity of the myometrium to the contractile effects of prostaglandins.
Mifepristone, also known as 11β-(4-(dimethylamino)phenyl)-17α-(1-propynyl)estra-4,9-dien-17β-ol-3-one, is a synthetic estrane steroid and a derivative of steroid hormones like progesterone, cortisol, and testosterone. It has substitutions at the C11β and C17α positions and double bonds at the C4(5) and C9(10) positions
Mifepristone is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system. It is on the complementary list and is included with a special note "where permitted under national law and where culturally acceptable"