Emergency contraceptive pills are generally effective when used within 72 hours of sexual intercourse, and the earlier they are taken, the better the contraceptive effect. Emergency contraceptives generally achieve contraceptive effect through mechanisms such as inhibiting ovulation, changing the morphology and function of the endometrium, altering cervical mucus properties, and changing the function of the fallopian tubes. Emergency contraception is divided into mono-progestin and anti-progestin classes. Emergency contraceptive pills of the unilateral progestin class, which are mostly composed of levonorgestrel, are over-the-counter drugs. At present, the commonly used emergency contraceptive pills in China include norethindrone probationary tablets, methinylgestrol probationary contraceptive tablets No.1, norethindrone probationary contraceptive tablets, No.53 contraceptive pills, etc. The active ingredient of anti-progestational emergency contraceptive pill is mifepristone, which is a prescription drug. It should be noted that if you have intercourse during ovulation, oral emergency contraceptives may not be effective at this time if the ovaries have already ovulated or the egg has been fertilized. Emergency contraceptives contain high doses of progestin, which can cause nausea, vomiting, irregular vaginal bleeding, and in severe cases, menstrual disorders, making them unsuitable as a daily contraceptive.