Withdrawal bleeding on birth control pills can last for 3 to 7 days, caused by the lowering of hormone levels, gradually decreasing, and those who bleed heavily should consult a doctor promptly. The main component of birth control pills is estrogen and progesterone, which can inhibit ovulation, inhibit the formation of fertilized eggs and the role of implantation. Contraceptive withdrawal bleeding is mainly due to the hormone level is reduced, the endometrium shedding formation, usually less bleeding. Retreating bleeding usually occurs after taking oral contraceptives, but the time of retreating bleeding will not last long, and the amount of bleeding will be significantly reduced and disappear within 3 to 7 days. If the withdrawal bleeding lasts for more than a week and is heavy, it is necessary to consult a doctor in time to determine whether there is a possibility of pregnancy and whether there is any lesion of the endometrium through the examination, and if necessary, it is necessary to give medication to stop bleeding, such as tranexamic acid or Anlocaine, etc., under the guidance of the doctor.