Mifepristone abortion drug molecule. Computer model of a molecule of mifepristone (ru486), an abortion- inducing drug. Atoms are represented as rods and are colour-coded: carbon (green), hydrogen (white), oxygen (red) and nitrogen (blue). Mifepristone belongs to a class of drugs known as selective progesterone receptor modulators. It is similar to the hormone progesterone, which is essential to maintain a pregnancy. When taken by a pregnant woman it binds to cells in the same manner as progesterone, thereby blocking the effects of the hormone. The drug is taken on its own in the early stages of pregnancy (up to about 8weeks), but in later stages its use must be combined with a drug to induce contraction of the uterus and expulsion of the foetus.