For the first to take contraceptive pills and then coitus has no effect, if oral short-acting contraceptive pills have been more than 7 days, the contraceptive effect may reach 99%. However, if oral emergency contraceptive drugs, this time there is no way to play a contraceptive role, because emergency contraceptive drugs can only be taken orally within 72 hours after the event to prevent, the principle is to inhibit the entry of sperm, so that the cervical tube mucus thickens, hindering sperm to enter, so as to achieve the purpose of contraception, if the oral beforehand, it will not play a very good contraceptive effect. If you need contraception, you need to take it orally within 72 hours afterward. Emergency contraceptive pills in the oral, must choose fasting or 2 hours after meals can be oral, so as not to reduce the effect of emergency contraceptive drugs.