[Mifepristone--a controversial drug with great potential].

BACKGROUND: Antiprogestins, agents that inhibit the action of progesterone, are among the most controversial and yet the more interesting therapeutic compounds developed over the past 20 years. MATERIAL AND METHODS: We present a review of the literature identified through limited searches on Medline, Cochrane and the Internet, with a discussion of the biological, clinical, political and ethical aspects of this important drug. RESULTS: The first effective antiprogestin in clinical use was mifepristone (also known as RU 486). This agent provides the most effective and safest means of medical abortion. It may also be used as a contraceptive and delivery-inducing agent and in the treatment of spontaneous abortion, ectopic pregnancies, leiomyoma, endometriosis, intrauterine fetal death, Cushing's syndrome and progesterone-dependent malignancies. INTERPRETATION: The introduction of mifepristone as an abortion-inducing agent has created intense political, ethical and moral controversies which have delayed clinical investigations and evaluations for potential expanded use.