How well does emergency contraception work?
When used correctly, emergency contraceptive pills (ECPs) work very well at preventing pregnancy. Consider that about 8 in 100 women who have unprotected sex one time during the fertile part of their cycle will become pregnant. If these 100 women take progestin-only ECPs (like Plan B), about 1 will become pregnant. If 100 women take ECPs with estrogen and progestin, about 2 will become pregnant. The IUD works even better. Only 1 in 1,000 women who have an IUD put in after having unprotected sex will become pregnant. The sooner you use emergency contraception after unprotected sex, the more likely it will prevent pregnancy. But you must use it correctly. For regular birth control pills used as ECPs, take the first dose within 3 days of having unprotected sex, but no later than 5 days. Take the second dose 12 hours later. For Plan B, both pills can be taken at the same time.
