After sex, if you do not take effective contraceptive measures, you can take emergency contraceptive pills within 72 hours, emergency contraceptive pills are mainly levonorgestrel and mifepristone. Levonorgestrel is a highly effective progestin, which can inhibit ovulation after oral intake and make the endometrium less tolerant, so it can cause non-pregnancy. Mifepristone is a progesterone antagonist, so after oral administration, it can counteract the progesterone in the body, if the progesterone is lowered, the fertilized egg will not be able to land, and will not be able to develop successfully, so it can also play a role in contraception.