The 72-hour emergency contraceptive pill can delay menstruation. 72-hour emergency contraceptive pills work by inhibiting ovulation and may cause a prolonged menstrual period if ovulation is staggered. 72-hour emergency contraceptive pills work by inhibiting the repair of the uterine lining, inhibiting the fertilized egg from being laid, and delaying ovulation, causing staggered ovulation to achieve contraceptive effects. The emergency contraceptive pill may cause ovulation to be delayed and ovulation to be avoided, so the clinical manifestation may result in delayed menstruation. It should also be noted that in case of failure of emergency contraceptive pills, it may also cause unintended pregnancy, and if there is an unintended pregnancy, it may also manifest as delayed menstruation, so clinically, if there is delayed menstruation, it is recommended that blood HCG measurement should be done to avoid unintended pregnancy caused by failure of emergency contraceptive pills.