After taking the pill, most people will experience withdrawal bleeding in about 3-5 days after stopping the pill. This kind of withdrawal bleeding is relatively small, and will be cleared up on its own in about 3-5 days, which is mainly caused by the side effects of the birth control pill. Contraceptive pills are highly effective progestins, which will cause the endometrium to thicken abnormally after oral intake. When the pills are stopped, the endometrium will lose the support of exogenous progestins, and retractive bleeding will occur, which is the main side effect of contraceptive pills. However, not all people who take birth control pills experience withdrawal bleeding, mainly because if they take the pill during the first half of their menstrual period, they will experience withdrawal bleeding. If the pill is taken during the second half of the menstrual period, withdrawal bleeding does not necessarily occur, but it does not indicate a contraceptive failure.