The 72-hour emergency contraceptive pill should be taken within 72 hours of having sex. The earlier it is taken, the more effective it is and should be taken as early as possible, one hour after sex. Taking the pill will stimulate the estrogen and progesterone levels in your body and may cause withdrawal bleeding for a week or so, and may cause your next period to come early or be delayed. If menstrual disorders occur, it usually takes 2-3 menstrual cycles to recover, which means that the last 2-3 menstrual cycles may be early or delayed, all of which are side effects of the emergency contraceptive pill. You should pay attention to rest, regular diet, sleep and other self-regulation, and observe the recent menstrual situation. If the menstrual period is disrupted for a longer period of time, medication is needed to regulate it if necessary.