Contraceptive pills refer to medications that are taken orally by women to prevent pregnancy. These pills work by regulating hormones in a woman's body, primarily through the use of estrogen and progestin (synthetic versions of female sex hormones). There are two main types of contraceptive pills: combination pills and minipillls. Combination pills contain both estrogen and progestin, while minipills only contain progestin. Both types of pills work by preventing ovulation (the release of an egg from the ovaries), thickening cervical mucus to block sperm from entering the uterus, and thinning the lining of the uterus so that a fertilized egg cannot implant itself. When taken consistently and correctly, contraceptive pills are highly effective in preventing pregnancy.