Mifepristone

Mifepristone, sold under brand names including RU-486, is a synthetic steroid with antiprogestational and antiglucocorticoid properties. It is used to terminate early intrauterine pregnancies in combination with misoprostol, and in some countries to treat endogenous Cushing's syndrome in adults.

Mechanism: Mifepristone binds to progesterone receptors with high affinity, blocking progesterone signaling required to maintain pregnancy. This causes decidual breakdown, cervical softening, and abortion when followed by uterotonic misoprostol.

Administration and efficacy: The standard regimen for medical abortion is mifepristone 200 mg orally, followed by misoprostol 800 µg within 24–48 hours. For pregnancies up to about 10 weeks gestation, this regimen achieves successful abortion in about 95–98% of cases, depending on gestational age and method of follow-up. The regimen is typically administered under medical supervision; availability and protocols vary by country.

Safety and contraindications: Common side effects include vaginal bleeding, cramping, nausea, and fatigue; serious complications are rare but can include heavy bleeding, infection, or an incomplete abortion requiring surgical intervention. Mifepristone is contraindicated in ectopic pregnancy or when pregnancy location is uncertain, in women with known allergy to the drug, and in individuals with significant adrenal insufficiency or those on prolonged systemic corticosteroid therapy without medical supervision. Use requires informed consent and appropriate medical oversight.

Regulatory and history: Development in the 1980s–1990s; approved by the U.S. FDA in 2000 for medical abortion, and later for other indications. It is available in many countries under regulatory controls, often within a formal abortion care pathway.