The emergency contraceptive pill is a hormonal medication and may cause a delay in menstruation for a period of 7-10 days. However, if there is withdrawal bleeding, which is a small amount of bleeding, after taking the oral emergency contraceptive pill, the bleeding may last for about 3-7 days. If there is retreating bleeding, the endometrium will shed a small amount at this time, causing a delay in menstruation that may take longer, perhaps half a month. If the period is delayed for more than a month, it is recommended to take an early pregnancy test to rule out the possibility of conception. Because the emergency contraceptive pill is not 100% contraceptive, there is a 20% chance of failure, so you can rule it out. If there is no pregnancy, when the delay is longer than the time, you should go to the hospital to do an ultrasound to see the thickness of the endometrium, and depending on the situation, you can be prescribed some menstrual drugs to stimulate menstruation.