The root cause of bleeding after taking the emergency contraceptive pill is withdrawal bleeding caused by ischemia, necrosis and shedding of the endometrium. The endometrium will gradually proliferate under the action of estrogen in the body, and will change from the proliferative state to the secretory state under the action of progesterone when it reaches a certain thickness. After taking the emergency contraceptive pill, the progesterone level in the body will increase rapidly, causing the endometrium to change to the secretory phase. After the emergency contraceptive pill is metabolized, the progesterone level drops rapidly again, which will cause the endometrium to lose the effect of progesterone and undergo necrosis, shedding and bleeding, which is a relatively common symptom after taking the emergency contraceptive pill and belongs to progesterone withdrawal bleeding, equivalent to a menstrual flow. Generally speaking, the better the endometrial hyperplasia, the more bleeding caused by taking the emergency contraceptive pill. Irregular vaginal bleeding may also occur after taking the pill, which is a common adverse reaction to the drug and may be observed. Generally speaking, there is no significant effect on the next menstrual cycle.