Emergency contraception is most effective when taken as soon as possible after unprotected sex. Depending on the type of emergency contraceptive pill, it should be taken within 72 hours (levonorgestrel) or up to 120 hours (ulipristal acetate) after the incident. If you're considering the copper IUD, it can be inserted within five days of unprotected intercourse. The sooner you take or use emergency contraception, the higher the likelihood of preventing pregnancy.