Mifepristone blocks progesterone, which is needed for development of the uterine lining in preparation for pregnancy. By doing this, it can prevent implantation. Mifepristone cannot prevent fertilization. EHC cannot terminate an already existing pregnancy.
Mifepristone can both prevent implantation and terminate a pregnancy after implantation.
A surgical abortion procedure would have to be performed if the pregnancy was not terminated through the use of medications alone. Medical abortion must be done under the supervision of a physician. The FDA has approved the use of mifepristone according to a specific protocol. Patients must sign a patient agreement and agree to return for subsequent visits. If an alternative protocol is being followed, the patient must sign an agreement for the alternative regimen as well.