In clinical practice, irregular vaginal bleeding may occur no matter taking short-acting contraceptive pills or emergency contraceptive pills. The main reasons are as follows: First, if you take the short-acting contraceptive pill, which is a combination of estrogen and progestin in clinical practice and can inhibit ovulation, it will cause endocrine disruption, which will lead to irregular vaginal bleeding. Most of this bleeding is small and will improve with continued use. If the bleeding does not improve after taking the pill, it is recommended to treat the symptoms, such as oral hemostatic drugs. Second, taking emergency contraceptive pills can cause vaginal bleeding, mainly because emergency contraceptive pills are highly effective progestin, which can cause abnormal thickening of the endometrium, and when the pills are stopped, the endometrium loses the support of exogenous progestin, and withdrawal bleeding will occur.