Levonelle 1500 is an emergency contraceptive that can be used within 72 hours (3 days) of unprotected sex or if your usual contraceptive method has failed. Levonelle is appropriate for use when: No contraception was used during sexual intercourse (tablet or barrier).The contraception measure was used incorrectly, for example as if a condom tore, slipped away or used in a wrong way.If vaginal pessary or diaphragm changed position, burst, was broken or taken out ahead of time. Levonelle 1500 contains a synthetic hormone like active substance called levonorgestrel. It prevents about 84% of expected pregnancies when you take it within 72 hours of having unprotected sex. It will not prevent a pregnancy every time and is more effective if you take it as soon as possible after unprotected sex. It is better to take it within 12 hours rather than delay until the third day. Levonelle 1500 is thought to work by: Stopping your ovaries from releasing an egg; preventing sperm from fertilising any egg you may have already released. Levonelle 1500 can only prevent you becoming pregnant if you take it within 72 hours of unprotected sex. It does not work if you are already pregnant. If you have unprotected sex after the use of Levonelle 1500 (during the same menstrual cycle), the tablet will not exert its contraceptive effect and there is a chance of pregnancy occuring.