What is the primary mode of action of mifepristone in a medical abortion?

Mifepristone is primarily recognized for its role in medical abortion due to its ability to block progesterone receptors. Progesterone is a crucial hormone necessary for maintaining pregnancy; it prepares the endometrium for implantation and supports the gestation process. By blocking these receptors, mifepristone effectively halts the actions of progesterone, leading to a breakdown of the endometrial lining. This process is critical, as the disruption of the endometrium prevents the implantation of a fertilized egg, thereby facilitating the termination of pregnancy.

Additionally, it is important to note that mifepristone is often used in conjunction with another medication called misoprostol, which induces uterine contractions and further facilitates the expulsion of the pregnancy. However, the primary mechanism of mifepristone itself lies in its antagonistic action on progesterone receptors, prompting the necessary physiological changes for a medical abortion.