There is no medical limit on how many times you can take Plan B in a year. It won’t cause long-term health problems or affect your future fertility, and it’s safe to take more than once, even within the same menstrual cycle. That said, it’s designed as a backup, not a primary method of birth control, and there are practical reasons why relying on it regularly is a bad strategy.
Why There’s No Hard Number
No major medical organization sets a maximum number of times you can take Plan B per year. It’s a single dose of a synthetic hormone (the same type found in many daily birth control pills, just at a higher dose), and your body processes it quickly. A systematic review of repeated emergency contraception use found limited evidence overall but “does not suggest safety concerns” with taking it multiple times.
So if you’ve taken it twice in a month or several times this year, you haven’t done anything dangerous. The concern with frequent use isn’t safety. It’s effectiveness and reliability.
Why It’s a Poor Substitute for Regular Birth Control
Plan B fails between 0.6% and 3.1% of the time per use. That might sound low, but those odds compound quickly if you’re relying on it cycle after cycle. Compare that to a copper IUD used as emergency contraception, which has a failure rate below 0.1%, or daily birth control pills, which are far more reliable when taken consistently.
Plan B also only works well in a narrow window. Its primary mechanism is delaying ovulation, and research shows it’s highly effective when taken before ovulation occurs. But if you’ve already ovulated or are within about two days of ovulating, the drug doesn’t delay the process at all. One study found that when given on the day before or the day of ovulation, over 90% of women still ovulated normally. That means the timing of your cycle matters enormously, and you rarely know exactly where you are in it.
What Frequent Use Does to Your Period
The most noticeable effect of taking Plan B repeatedly is menstrual disruption. Your next period after a dose may come earlier or later than expected, and the flow can be heavier, lighter, or spottier than usual. A single use might shift things by a few days. Frequent use, though, can make your periods genuinely unpredictable, which makes it even harder to track your cycle or know when you might be fertile.
This irregularity is temporary and not a sign of harm. Your cycle will normalize once you stop taking it frequently. But unpredictable periods can add stress and make it difficult to tell whether the pill worked or whether you might be pregnant.
One Risk Worth Knowing About
A recent systematic review flagged one finding: among women who became pregnant after taking emergency contraception, those who had used it multiple times in the same cycle had roughly 2.5 times higher odds of an ectopic pregnancy (where the embryo implants outside the uterus) compared to those who used it once. The evidence is limited and rated very low certainty, but ectopic pregnancies are a medical emergency. If you’ve taken Plan B more than once in a cycle and experience sharp lower abdominal pain, shoulder pain, or unusual bleeding, get evaluated promptly.
Weight Can Reduce Effectiveness
Plan B becomes less effective at higher body weights. Health Canada, the only regulator to put specific numbers on this, states that levonorgestrel-based emergency contraception may be less effective in women over 165 pounds and potentially ineffective over 176 pounds. Other experts have pushed back on the “ineffective” threshold, noting there’s still some benefit, but the decline is real.
For women with a BMI over 30, a different emergency contraceptive pill (sold under the brand name ella) roughly cuts the failure risk in half compared to Plan B, from about 6% down to 2.5%. A copper IUD remains the most effective emergency option regardless of weight.
Switching to a Regular Method
If you’re finding yourself reaching for Plan B frequently, that’s a signal to explore a regular contraceptive method. You can start hormonal birth control right after taking a Plan B dose if you’re a new or returning user. If you were already on the pill and needed Plan B because of a missed dose, you can simply resume your regular schedule.
One important detail: after starting or restarting hormonal birth control following emergency contraception, you’ll need to use condoms or abstain for the first seven days while the method becomes effective. If you took ella instead of Plan B, wait until the sixth day after your dose before starting any hormonal method, because the two can interfere with each other.
The bottom line is straightforward. Taking Plan B multiple times in a year won’t hurt you, but each time you use it, you’re gambling on a method that’s significantly less reliable than everyday options. It works best as what its name implies: a backup plan.