There are actually no particularly serious side effects to taking the pill once: first, it may cause abnormal uterine bleeding. Vaginal bleeding may occur within 3-7 days after taking the pill, which can lead to disruption of the menstrual cycle, usually returning to normal after 1-2 months. Second, it will cause the increase of menstrual volume, the withdrawal bleeding after taking the pill, equivalent to a drug diagnosis, the patient will have increased menstrual volume, abdominal pain and other symptoms. Thirdly, it can cause abnormal ovulation. The pill can cause changes in the menstrual cycle and also in the ovulation time. Therefore, in the absence of fertility requirements, patients are not recommended to take oral contraceptives to prevent pregnancy, and can use condoms to achieve the purpose of contraception.