How effective is emergency contraception?
When used perfectly, emergency contraception (EC) is effective at preventing pregnancy, but it is not as effective as some other methods of contraception, such as the birth control pill. It also does not protect you against HIV/AIDS and other STDs, like condoms do. On average, if 100 women have unprotected intercourse once during the second or third week of their cycle, 8 will become pregnant. Following treatment with combined EC (such as high doses of certain birth control pills), 2 will become pregnant (a 75% reduction in the risk of pregnancy); following treatment with progestin-only EC (Plan B), 1 will become pregnant (an 89% reduction in the risk of pregnancy). An IUD can be inserted as emergency contraception, and it reduces the risk of pregnancy by more than 99%. If a woman uses Plan B perfectly after every act of unprotected sex, and uses no other method of birth control for a year, then her annual risk of pregnancy would be about 19%.
