 Step one. At the abortion facility or at home, the woman swallows mefepristone pills. Mefepristone blocks the action of a hormone called progesterone. That the American people should have access to that medication. Progesterone is naturally produced in the mother's body to stabilize the lining of the uterus. When mefepristone blocks progesterone, the lining of the mother's uterus breaks down, cutting off oxygen and vital nutrients to the embryo, who then dies inside the mother's womb.