Plan B helps prevent pregnancy by temporarily delaying ovulation. It must be taken within 72 hours (3 days) after unprotected sex or birth control failure. The sooner it is taken the better it works. You can buy Plan B right off the shelf in the Family Planning aisle at Walmart in all 50 U.S. states. There is no ID or age restriction required for purchase. You can also buy Plan B online and pickup curbside or in-store. It should not be used as regular birth control. Plan B will not impact your ability to get pregnant in the future.