Taking emergency contraceptive pills may trigger delayed menstruation, but due to the existence of individual differences, this situation is different from person to person. Progesterone is a common component of emergency contraceptive pills, and its main function is to increase uterine blood flow, promote changes in the secretion phase of the uterine lining, thereby inhibiting ovulation, and increase the viscosity of the cervical mucus. Therefore, after taking the emergency contraceptive pill, on the one hand, will directly increase the resistance of sperm movement in the cervix to prevent the sperm and egg encounter, but also can prevent the fertilized egg successfully implanted to achieve the effect of contraception. Therefore, the process is there to affect the normal menstruation of the possibility of taking emergency contraceptive pills after the existence of early or delayed menstruation phenomenon. In addition to the possibility of delayed menstruation, nausea, vomiting, breast swelling and pain may also occur after taking emergency contraceptive pills. In severe cases, it can also cause abnormal bleeding from the uterus. Therefore, after taking the pill must be timely observation, if there is discomfort or abnormalities need to go to the hospital in time to avoid delaying the condition.