Effectiveness of Emergency Contraception

Emergency contraceptive pills (ECPs) that contain both estrogen and progestin are about 75% effective at keeping a woman from getting pregnant. ECPs that contain only progestin are about 89% effective. The Copper-T intrauterine device (IUD) is 99.9% effective. Timing is important to how well emergency birth control works. The sooner a woman gets emergency birth control after having unprotected vaginal intercourse, the better it works. If a woman is in the fertile part of her cycle (ovulating), or close to that time, when she uses emergency birth control, her chances of getting pregnant are greater.