Emergency contraceptive pills are useful within 24 hours, emergency contraceptive pills work as long as they are taken within 72 hours, but the success rate of emergency contraceptive pills can only reach 85%-90%, there are also about 10% of contraceptive failure after taking the pill, may be normal pregnancy, so the earlier you take it, the better the effect, if sex for more than 72 hours before taking it does not work. When taking the pill, do not eat or drink for 2 hours before and after to avoid reducing the efficacy of the drug. After taking the pill and stopping for 3-7 days, there will be withdrawal bleeding, if there is no withdrawal bleeding or very little bleeding, be alert to the failure of contraception, and if you do not come when you come to menstruation, go to the hospital in time to do a checkup to rule out unwanted pregnancy.