MIFEPREX ACTION MECHANISM Progesterone is a natural substance needed for your pregnancy to continue. Mifeprex is an anti-progesterone drug that works by disrupting uterine lining as a result, placenta will be deprived of nourishment. Embryo dies due to absence of oxygen and nourishment. Misoprostol is given on 3rd day after Mifeprex treatment, whic..