Whether it is useful to take one 72-hour emergency contraceptive pill is related to the effective dose contained in the drug, if it is 0.75mg of levonorgestrel tablets, you need to take an additional tablet 12 hours after taking the pill; if it is 1.5mg of levonorgestrel tablets, you can usually take one tablet. Emergency contraceptive pills are used for unprotected measures or other contraceptive methods for occasional errors, through the inhibition of ovulation and prevent the fertilization of the egg implantation, and make the cervical mucus consistency increases, sperm penetration resistance increases, so as to play the role of contraception, the specific need to take a few tablets should be based on the dosage of each piece of medication to decide. Women may experience nausea, vomiting, breast swelling and pain, menstrual disorders and other discomforts after taking the medication. It is also important to note that it should be contraindicated for those who are allergic to the product, have impaired liver or kidney function, and have a history of breast cancer, high blood pressure, diabetes and other medical conditions. For women who do not want to have children, it is recommended that they use condoms, birth control devices and other means of contraception. If they need to take emergency contraceptive pills, it is recommended that they take them under the guidance of a professional doctor, and should not use them blindly.