A combination of hormones used in oral contraceptives (birth control pills). Mestranol and norethindrone (Necon, Norinyl, Ortho-Novum) are both female hormones involved in contraception; one is a form of estrogen and the other a form of progesterone. These hormones prevent pregnancy by causing the woman’s cervical mucus to thicken, which makes it harder for sperm to reach the uterus and for an egg to implant in the uterus.