The difference between one pill and two pills is mainly emergency contraceptives, mainly in terms of dose, method of use and side effects. 1. dose: one pill is 1.5mg per pill, if two pills are 0.75mg per pill, the total dose is the same; 2. method of use: one pill is a one-time dose, two pills are taken after the first pill is taken. It is necessary to take another one after the first one is taken for 12 hours, but make sure that it is taken within 72 hours after sex; 3. Side effects: the side effects of the one-package pill may be greater in a short time, especially in the gastrointestinal tract, which may produce nausea, vomiting, loss of appetite, etc. The two-piece package of birth control pills may have relatively light side effects for a short time because of the smaller dose taken each time, and if the gastrointestinal function is weak, you can choose the two-piece package. However, there may not be much difference for side effects caused by hormonal increase or decrease like irregular menstruation. In addition, it should be noted that the emergency contraceptive pill can only work for this unprotected sex, and it can only be taken once in a menstrual cycle, and if you have sex again after this cycle, you still need to take other reliable contraceptive measures.