Intercourse activities can take place in the heat of the moment and hence the cases of unplanned and unprotected intercourse are no less in the world. When you buy Plan B or similar emergency contraceptive, it effectively prevents the implantation in your body, thereby preventing an unwanted pregnancy despite having unprotected sexual intercourse. The sooner the pill is consumed, the better effectiveness will it show. And hence women are suggested to use it at the earliest after having an unprotected intercourse. The pill is typically administered in following cases: Missed your birth control Torn condom The condom has slipped out