The most used contraceptive product in the united states is the birth control pill. Many combination birth control pills (marketed under various names including ovral, tetragynon and triphasil) are also being used for post coital contraception. Mifepristone is an antihormone that when taken during the first seven weak of pregnancy in conjunction with a tiny amount of prostaglandin to stimulate uterine contraction induces miscarriage by blocking progesterone's quieting effect on the uterus. For several years the second most used contraceptive method was the intrauterine device a plastic or metal device inserted into the uterus that prevented the fertilized egg from implanting in the endometrial lining.