Emergency contraceptive pills are useful when taken one hour after sex, and can be taken under doctor’s supervision. Emergency contraceptive pill is used for emergency contraception after unprotected sex, to be taken within 72 hours of sex is effective, so taking it after one hour of sex is useful, but there will be contraceptive failure. Side effects such as nausea, vomiting and irregular vaginal bleeding may occur after taking the pill, which generally do not need to be treated, and should be used under the guidance of a doctor. Emergency contraceptive pills can only be effective for one sexual intercourse, and you still need to take contraceptive measures if you have sex again after taking the pills. Because the hormone dose of emergency contraceptive pills is large and the contraceptive effectiveness rate is lower than that of regular contraceptive pills, frequent use is not recommended. It is useful to take emergency contraceptive pills one hour after sex, but if your period is delayed for more than one week after taking the pill, you still need to rule out the possibility of pregnancy.