Mifepristone (or RU-486) is a synthetic, steroidal antiprogestogen and antiglucocorticoid pharmaceutical drug. It is a 19-norsteroid with substitutions at positions C11 and C17 (17β-hydroxy-11β-(4-(dimethylamino)phenyl)-17α-(1-propynyl)estra-4,9-dien-3-one), which antagonizes cortisol action competitively at the receptor level.Mifepristone is a low-efficacy partial agonist of the progesterone receptor used as an abortifacient in the first months of pregnancy, and in smaller doses as an emergency contraceptive. It is also a glucocorticoid receptor antagonist to a lesser extent, and has occasionally been used in refractory Cushing's syndrome (due to ectopic/neoplastic ACTH/cortisol secretion). During early trials, it was known as RU-38486 or simply RU-486, its designation at the Roussel Uclaf company, which designed the drug. The drug was initially made available in France, and other countries then followed—often amid controversy. It is marketed under tradenames Korlym and Mifeprex, according to FDA Orange Book.Mifepristone was the first antiprogestin to be developed and it has been evaluated extensively for its use as an abortifacient. The original target for the research group was the discovery and development of compounds with antiglucocorticoid properties. These antiglucocorticoid properties are of great interest in the treatment of severe mood disorders and psychosis, although a review of published articles was inconclusive on their efficacy, and considered the use of these drugs in mood disorders at 'proof of concept' stage. It is on the WHO Model List of Essential Medicines.