Birth control pills are effective when taken within 72 hours of intercourse, and the sooner you take them, the better the results. If you have intercourse during ovulation, it is best to take the emergency contraceptive pill within 24 hours to maximize the effectiveness of contraception. Later, as time passes, the effectiveness of the pill decreases, and the success rate is only 50% when the pill is taken at 72 hours. It is best to take the pill immediately after intercourse for the highest contraceptive success rate, but the effect of taking it afterwards is much worse. It is best to take the pill on an empty stomach, so that the drug can be absorbed more completely and achieve the full effect of contraception. If you have a serious gastrointestinal reaction due to your physical condition, you should take it half an hour after a meal to reduce the side effects of the pill.