Plan B can be taken as often as needed for emergency contraception. There is no known limit on the number of times it can be safely used, even more than once in the same menstrual cycle. However, Plan B is designed for emergency use after unprotected sex or birth control failure and is not recommended as a regular form of birth control. Frequent use may cause side effects like menstrual changes, headache, or abdominal pain, and it is less effective than standard long-term contraceptive methods. For regular contraception, other methods like birth control pills or IUDs are advised. Plan B does not protect against sexually transmitted infections (STIs).