Emergency contraceptive pills are effective when taken 24 hours after sex. Emergency contraceptive pills are taken within 72 hours after sex, and the earlier they are used, the more effective they are in relative terms. Emergency contraceptive pills are only a remedy after unprotected sex, definitely not a common method of contraception, usually still need to do a good job of standardized contraception. The use of emergency contraceptive pills, the probability of contraceptive success and other normal contraceptive methods compared to the difference, the contraceptive effect will be poor, after taking the pill has led to contraceptive failure or the probability of ectopic pregnancy, in addition, emergency contraceptive pills on menstruation will also have a certain effect. Therefore, without special circumstances, generally try not to use, the number of times within a year to use emergency contraceptive pills is recommended no more than twice.