Does plan b work if taken before unprotected sex?

Bad idea: Plan B works by blocking ovulation; once it wears off ovulation continues. If you have sex, the sperm sticks around, and once the pill wears off, the egg will come into contact with them once released (you actually increase your chances of getting pregnant). To really prevent pregnancy, best to use condoms and a second method such as BC pills every single time (why take a chance?)