Ethinyl estradiol birth control pills contain two types of female hormones, estrogen and progesterone.
Ethinyl estradiol pills work to prevent pregnancy in three different ways: First, by preventing the release of an egg from the ovaries (preventing ovulation); second, by increasing the thickness of the mucus in the cervix, making it difficult for sperm to enter the uterus; and third, by thinning the lining of the uterus, making it difficult for an egg to attach to it.