Levonelle 1500, commonly known as the morning-after pill, is an emergency contraceptive intended to prevent pregnancy after unprotected sex or if a contraceptive method has failed. The active ingredient in Levonelle 1500 is levonorgestrel, a synthetic version of the natural hormone progesterone. It works primarily by stopping or delaying the release of an egg from the ovary. It may also prevent the fertilization of any egg that may have already been released or prevent a fertilized egg from attaching to the womb lining. Levonelle 1500 is most effective when taken as soon as possible after unprotected intercourse, ideally within 12 hours, but it can still be used up to 72 hours (3 days) afterward. It is a single-dose tablet, which makes it convenient to use. However, it's important to note that Levonelle 1500 is not intended as a regular method of contraception and should not be used as such.