Emergency contraceptive pills taken orally twice in a row may have certain side effects. Common ones include withdrawal bleeding, early menstruation, delayed menstruation, and irregular vaginal bleeding, while other symptoms include nausea, vomiting, breast swelling and pain, headache, dizziness, abdominal pain, and fatigue. The presence or absence of withdrawal bleeding after taking the pill is not a sign of success or failure of contraception. Although pregnancy is unlikely after taking the pill, the contraceptive effect of the emergency contraceptive pill is not 100%. The contraceptive mechanism of the emergency contraceptive pill is to inhibit ovulation, prevent the pregnant egg from implanting, and increase the consistency of cervical mucus, increasing the resistance to sperm penetration and affecting the uterine lining, so as to play a fast-acting contraceptive effect. It is important to note that after taking emergency contraceptive pills, you need to take contraceptive measures when having sex again, otherwise you will easily get pregnant.