Breast swelling and pain a week after taking emergency contraceptive pills is caused by the drug, because emergency contraceptive pills are a kind of highly effective progestin, this kind of drug can appear breast enlargement, can also cause the fluctuation of hormones in the body, so there will be breast swelling and pain. Usually about a week after stopping the pill, there will be withdrawal bleeding, after taking the pill withdrawal bleeding, breast swelling and pain will be significantly reduced or disappear. Emergency contraceptive pills can cause endocrine disorders, and are prone to dysmenorrhea or breast tenderness, which are relatively common phenomena. Therefore, the emergency contraceptive pill should not be used as a regular contraceptive. Because this drug can not be taken more than 3 times a year, not more than 2 times a month, otherwise it will cause endocrine disruption.