Birth control pills include long-acting pills, short-acting pills and emergency contraceptives. Taking different birth control pills has a slightly different effect on menstruation, which may be early or delayed. Usually long-acting pills do not delay menstruation. The short-acting pill is not used for contraception, but also for regulating the menstrual cycle, and should be taken orally as prescribed. Some women may even experience menstrual disorders for 1-2 months if they take emergency contraceptives. However, most women experience a few days of early menstruation, which is called withdrawal bleeding, with slightly more menstrual flow and may last slightly longer than the usual menstrual period. There are also some women who experience delayed periods. If the delay is more than 1 week, you need to check with an early pregnancy test or go to the hospital to get a blood test for HCG to rule out pregnancy. The failure rate of emergency contraceptive pill is about 20%, and it may cause menstrual disorders, irregular vaginal bleeding and other symptoms, and in some women, ectopic pregnancy may occur.