mifepristone

mifepristone, synthetic steroid drug used together with misoprostol to induce abortion in the early weeks of pregnancy. Mifepristone is an antiprogestin—it exerts its effects by blocking the action of progesterone, a naturally produced hormone that prepares the inner lining of the uterus for implantation of a fertilized ovum and support of a growing embryo and placenta. Mifepristone is known by various other names, including RU-486, Mifegyne, and Mifeprex.

Mifepristone is taken orally in a prescribed dose during the first 7–10 weeks of pregnancy. Immediately after taking mifepristone or up to 48 hours later, it is followed by a dose of the synthetic prostaglandin misoprostol. Typically, within two days of initiating treatment, the uterine lining begins to deteriorate, accompanied by bleeding and cramping similar to that experienced during normal menstruation. The embryo and other uterine contents are expelled in a process very similar to spontaneous abortion, or miscarriage. In a small number of cases the induced abortion is not complete and must be followed by a surgical procedure, most commonly vacuum aspiration.

Mifepristone is relatively safe for women and can be administered easily and privately at health clinics, including those that are not equipped for surgical abortions. In some places, pills can be mailed and taken at home. The mifepristone dose is taken under medical supervision, but the prostaglandin can be administered at home, where the contractions and expulsion also take place. The most common side effects of mifepristone are the usual symptoms of miscarriage: cramping, bleeding, and occasional nausea, dizziness, and back pain. The drug does not reliably terminate pregnancies beyond the early weeks, and it is not prescribed for an ectopic pregnancy (when a fertilized ovum is implanted outside the uterus—for instance, in one of the fallopian tubes).

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Mifepristone was developed by the French pharmaceutical company Roussel-Uclaf in the 1980s. Under the name RU-486, it entered the market in France in 1988. Since then it has been approved for use in countries worldwide, including the United States in 2000. In the mid-2020s medical (medication) abortion accounted for the majority of abortions in the United States.