Morning-after pills, also known as emergency contraceptive pills, are a type of medication used to prevent pregnancy after unprotected sex or contraceptive failure. They are most effective when taken within 72 hours (3 days) of unprotected sex, but can still be effective up to 5 days (120 hours) after sex.
Morning-after pills work by preventing or delaying ovulation (the release of an egg from the ovary). They can also prevent fertilization of the egg by sperm or implantation of a fertilized egg in the uterus. Morning-after pills do not terminate a pregnancy that has already begun.