Oral contraceptives, better known as birth-control pills, are taken to prevent pregnancy. They come in packets of 21, 28, or 91 tablets and are generally taken by mouth once a day, every day or almost every day of a regular cycle. Birth control pills come in different formulations, but they generally either contain progestogen or a combination of estrogen and progestogen. Birth control pills work by preventing ovulation. If no egg is released, pregnancy cannot occur.
