Menstruation after taking birth control pills is mainly due to changes in hormone levels in the female body after taking the pills, resulting in shedding of the uterine lining. The most common is to take long-term contraceptive drugs, mainly taking progestin, suddenly stopping the drug will lead to endometrial withdrawal bleeding, bleeding is not much, will not be accompanied by other uncomfortable symptoms. Vaginal bleeding after taking contraceptives also need to be alert to the possibility of pregnancy, if pregnant, taking drugs may lead to abortion and other accidents, you need to pay attention to the presence of abdominal pain, but also need to carry out timely early pregnancy check, can effectively avoid the occurrence of accidents. If you usually take contraceptives for a long time, you need to pay attention to take the pill on time and according to the dosage, avoid stopping or reducing the dosage on your own, mainly to avoid unintended pregnancy as well as lead to serious adverse reactions.