Bleeding after a few days after taking birth control pills may be caused by withdrawal bleeding, menstrual flow, pre-menstrual abortion and other conditions caused by the drug. 1. Withdrawal bleeding: the function of the uterus is regulated by the body’s secretion of estrogen and progesterone, contraceptive pills contain estrogen and progesterone components, the body’s estrogen and progesterone content increases after the use of the drug, so that the lining of the uterine cavity is transformed into a proliferative phase state, such as contraceptive pills in the body to fully metabolize the hormone content declines, it will be in the use of the drug after the vaginal bleeding, which is also known as withdrawal bleeding. 2. Menstruation: Bleeding a few days after taking birth control pills may be normal menstruation, but also changes in hormone levels in the body, the endometrium stripped of a physiological process. 3. Pre-eclampsia: Failure of contraception after taking the pill can lead to unwanted pregnancies, and after an unwanted pregnancy the fertilized egg is deposited in the uterine cavity, and pre-eclampsia may cause a small amount of vaginal bleeding. Bleeding a few days after taking birth control pills, observing heavy bleeding and prolonged bleeding time, go to the hospital to check the cause of treatment.