For girls who have been taking birth control pills have not come to menstruation, first of all, it depends on what kind of birth control pills and the time of taking the pills, if you have been taking short-acting oral contraceptives, this kind of contraceptive pills contain hormone components, if you eat for several months or even years, in this case, it may lead to not having a menstrual period, because the contraceptive components of the pill can inhibit the female hypothalamus and pituitary gland from secreting hormones. However, this condition usually improves when the pill is stopped. If the emergency contraceptive pill is the cause of the absence of menstruation, the possibility of pregnancy should be ruled out, because the contraceptive efficiency of the emergency contraceptive pill is not 100%, and some women who take such a contraceptive pill may still become pregnant.