There is no hard limit on how many times you can take Plan B. The World Health Organization states that repeated use poses no known health risks, though side effects like irregular bleeding become more common the more often you use it. That said, Plan B is significantly less effective at preventing pregnancy than regular birth control, which is why it’s designed as a backup, not a primary method.
No Medical Cap, but More Side Effects
You can take Plan B more than once in the same menstrual cycle if needed, and there is no maximum number of times per year that makes it medically dangerous. The WHO is clear on this point: repeated use does not cause known health risks and does not harm future fertility.
What does change with frequent use is how you feel. Plan B delivers a large dose of a hormone that can delay your period by up to a week, cause spotting between periods, heavier menstrual bleeding, nausea, and fatigue. Taking it multiple times in a short window stacks those side effects. Your cycle can become unpredictable for weeks, making it harder to know when you’re fertile and harder to tell whether the pill actually worked. If your period doesn’t arrive within three weeks of taking Plan B, take a pregnancy test.
One important caveat: for people with certain health conditions that make hormonal contraception risky (blood clotting disorders, for example), frequent use may carry additional concerns. If that applies to you, a provider can help sort out safer options.
Why It’s a Poor Substitute for Regular Birth Control
The practical reason not to rely on Plan B isn’t safety. It’s math. Plan B is up to 89 to 90 percent effective when taken within 72 hours of unprotected sex. That sounds high until you compare it to what’s available for daily use: the birth control pill, patch, or ring are about 91 percent effective with typical, imperfect use and 99 percent with perfect use. An IUD or implant is close to 100 percent effective, and you don’t have to remember to do anything.
Put another way, if Plan B were your only method and you used it after every act of unprotected sex over a year, your odds of pregnancy would be considerably higher than if you were on almost any form of regular contraception. And Plan B costs $30 to $50 each time, while many ongoing methods are covered by insurance or available at low cost.
How Plan B Actually Works
Plan B contains a single large dose of levonorgestrel, a synthetic hormone. Its primary job is to delay or prevent ovulation, the release of an egg from the ovary. If you haven’t ovulated yet when you take it, the pill suppresses the hormonal surge that triggers egg release, so there’s no egg available to be fertilized.
This is also why timing matters so much. Plan B works best when taken before ovulation. If you’ve already ovulated, the pill is essentially ineffective. FDA data confirm that when Plan B is taken after ovulation has occurred, pregnancy rates are no different from what you’d expect without any intervention at all. It does not prevent a fertilized egg from implanting.
Weight Affects How Well It Works
If your BMI is above 26, Plan B becomes less reliable. Research from Oregon Health & Science University found that levonorgestrel is the most likely emergency contraception option to fail in people with a higher BMI, because the hormone is sensitive to body weight. This doesn’t mean it does nothing, but the protection drops enough to matter. A copper IUD inserted within five days of unprotected sex is close to 100 percent effective regardless of weight, making it the strongest emergency option in that situation.
Starting Regular Birth Control After Plan B
If you’ve found yourself taking Plan B more than once or twice, that’s a signal to consider a method you don’t have to think about in the moment. The good news: you don’t have to wait until your next period to start. After taking Plan B, you can begin the pill, patch, ring, implant, or any other hormonal method immediately. You’ll need to use a backup method like condoms for the first seven days while the new method takes effect.
If you want an IUD, a copper IUD can be placed the same day you take Plan B with no backup needed. A hormonal IUD can also be placed right away, but you’ll need backup for seven days afterward.
If you took a different emergency contraceptive containing ulipristal acetate (sold as ella), the timing is slightly different: wait six days before starting any hormonal method, because the two medications can interfere with each other’s effectiveness.
An implant or IUD is worth considering specifically because they remove the daily decision-making that leads to gaps in protection. Both are reversible, last years, and are the most effective reversible contraception available.