RU 486 (mifepristone), developed in 1980, is an antiprogestin used to terminate pregnancies within the first 9 weeks by blocking progesterone's effects. The drug is commonly administered in combination with prostaglandins to induce uterine contractions and has been used in various countries, including France and the US, accounting for a significant percentage of abortions there. While generally safe, it is not suitable for all women, and some may experience side effects or complications requiring medical attention.