The presence of withdrawal bleeding after taking emergency contraceptive pills does not mean that the contraceptive is successful. Retreating bleeding is just a normal adverse reaction to taking emergency contraceptive pills. It is because the main ingredient of the pill is progesterone, the level of progesterone in the body will increase rapidly after taking the pill, and after a week the level of progesterone in the body will decrease rapidly, causing the endometrium to fall off, and withdrawal bleeding will occur. If the amount of withdrawal bleeding is relatively large after a week of taking the emergency contraceptive pill, and more than three days is the normal menstruation, indicating the success of contraception. If women do not have normal menstruation after the withdrawal bleeding, and have dizziness, fatigue, nausea, vomiting, chest distension and other reactions, usually the contraceptive is not successful, we need to do early pregnancy test to rule out the possibility of early pregnancy.