According to the search results, it is safe to take Plan B or other emergency contraception twice within the same menstrual period, and it is also safe to take it multiple times within an even shorter timeframe. However, it is not advised to take more than one morning-after pill at once, as it may cause more side effects like nausea and vomiting. Taking Plan B multiple times does not change its effectiveness, and it wont cause any long-term side effects. It is important to note that Plan B is not intended to be used as a regular method of birth control, as it is less effective than other types of birth control. Plan B can also temporarily change someones menstrual cycle, so it is difficult to predict when the next period will occur. In summary, while it is safe to take Plan B multiple times, it is not recommended to use it as a regular method of birth control.