You can take Plan B more than once, and there is no known medical danger or lifetime cap, but it is a poor substitute for regular birth control.
Each dose protects only against sex that already happened, and its 75 to 89% effectiveness within 3 days compounds into real pregnancy risk when used repeatedly. The other cost is your cycle: frequent use commonly makes periods irregular and unpredictable, and the label is direct that it is not for regular birth control. Two rules matter for repeat use. Never combine ella and Plan B within 5 days of each other, because they can reduce each other's effectiveness; if you need EC again within that window, use levonorgestrel again. And use backup contraception after any EC dose, since it covers nothing going forward. If you find yourself buying Plan B more than once or twice a year, treat that as the cue to pick a regular method; nearly all of them are more effective and most cost less than repeated EC.
What to do
Common questions
How often can you take Plan B?
There is no hard medical limit on how many times you can take Plan B, and taking it more than once, even in the same cycle, is not known to be dangerous. It does not cause infertility and does not lose all effect with repetition. But two real reasons keep it in the emergency lane. First, effectiveness: each use only covers the unprotected sex that already happened, and the typical-use protection (75 to 89% within 3 days) is far below what the pill, implant, or IUD delivers month after month. Relying on EC repeatedly adds up risk quickly. Second, your cycle: frequent levonorgestrel doses commonly make periods irregular and unpredictable, which is stressful in itself when you are worried about pregnancy. The label says it plainly: not for regular birth control. Two practical rules if you do need it again soon: do not take ella and Plan B within 5 days of each other (they can interfere; stick with levonorgestrel for the repeat), and use backup contraception afterward, since EC offers zero protection for sex that happens later. If you are reaching for Plan B more than once or twice a year, that pattern is the signal to set up a regular method, which is more effective, cheaper over time, and gentler on your cycle.