Certain birth control pills that can be used as an emergency method shortly after unprotected intercourse to prevent pregnancy. Birth control pills that contain estrogen and minipills that contain progestin can be taken in specific doses within 72 hours after sex. This inhibits or delays ovulation, reducing the chance of pregnancy by at least 75 percent. Alternatively, a copper IUD can be inserted up to five days after unprotected intercourse to reduce the chance of pregnancy by 99 percent. Keep in mind that these measures are not a substitute for traditional contraceptive methods; some women experience side effects such as nausea or vomiting. Visit The Emergency Contraception Website for more details.