It is useless to take emergency contraceptive pills a week after sex to prevent pregnancy, and it is impossible to achieve the effect of contraception. The sooner you take the pill, the better it works. Generally speaking, the pill should be taken within 72 hours after intercourse in order to effectively prevent pregnancy, and it is very likely that the sperm and the egg will have already combined to form a fertilized egg. If you do not take the pill in time, it is recommended that you observe whether your period is on schedule, and if it exceeds the normal time, you need to self-test or go to the hospital to check whether you are pregnant.