After taking the emergency contraceptive pill does not menstruation, if the time of stopping the drug is less than 7 days, consider that the time is too short for the reason, need to observe for a few more days. If more than 7 days after taking the drug, and also has passed the time of normal menstruation, should consider the possibility of contraceptive failure of contraceptive pill accidental pregnancy, need to go to the hospital in a timely manner, to do blood HCG laboratory tests to clarify the diagnosis. Emergency contraceptive pills can only be used as a remedial measure after contraceptive failure, the sooner you take it, the better the contraceptive effect, if more than 72 hours to take it, can not guarantee the success of contraception, and emergency contraceptive pills only to take the drug before the occurrence of sexual behavior has a contraceptive effect, and then there should be coitus should be taken to other effective means of contraception, such as condoms. If used correctly, the success rate of emergency contraception is very high.