Progesterone receptor antagonist

Antiprogestogen
Drug class
Mifepristone, an antiprogestogen that is used to induce medical abortions.
Class identifiers
Synonyms	Antiprogestins; Progesterone antagonists; Progesterone blockers
Use	Medical abortion, emergency contraception, uterine fibroids
ATC code	G03XB
Biological target	Progesterone receptor
Chemical class	Steroidal

Antiprogestogens, or antiprogestins, also known as progesterone antagonists or progesterone blockers, are a class of drugs which prevent progestogens like progesterone from mediating their biological effects in the body. They act by blocking the progesterone receptor (PR) and/or inhibiting or suppressing progestogen production. Antiprogestogens are one of three types of sex hormone antagonists, the others being antiestrogens and antiandrogens.

Antiprogestogens are used as abortifacients and emergency contraceptives and in the treatment of uterine fibroids. They are also being studied in the treatment of breast cancer. Examples of antiprogestogens include the progesterone receptor weak partial agonist mifepristone, the selective progesterone receptor modulator (SPRM) ulipristal acetate, and the silent antagonist aglepristone. For medical abortion, mifepristone is combined with a prostaglandin (e.g., gemeprost).