What is the mechanism of action of antiprogestins like Mifepristone?

• A. They enhance progesterone effects
• B. They block the effects of progesterone
• C. They stimulate estrogen production
• D. They inhibit estrogen receptors

Answer: (B)

Antiprogestins, such as Mifepristone, work by blocking the effects of progesterone. This mechanism is crucial in reproductive health, particularly in the context of medical abortions and managing conditions like Cushing's syndrome. By binding to progesterone receptors, Mifepristone prevents progesterone from exerting its effects, which is essential for maintaining pregnancy. When progesterone is blocked, the lining of the uterus can shed, leading to the termination of pregnancy. This action contrasts with the other options listed, where enhancing progesterone effects, stimulating estrogen production, or inhibiting estrogen receptors do not accurately describe the role of antiprogestins in the body. Thus, understanding that Mifepristone effectively negates the action of progesterone clarifies its therapeutic uses in women's health.