Plan B does not cause infertility, no matter how many times you take it. There is no known number of uses that will damage your fertility or reduce your ability to get pregnant in the future. This is one of the most common fears surrounding emergency contraception, and the research is clear: repeated use does not lead to permanent reproductive harm.
What the Evidence Actually Shows
The World Health Organization states it plainly: “Drugs used for emergency contraception do not harm future fertility.” There is also no delay in the return to fertility after taking it. Your body doesn’t accumulate damage from repeated doses.
A 2022 systematic review analyzed 33 studies on levonorgestrel (the active ingredient in Plan B) and found no effect on fallopian tube function, no increased risk of ectopic pregnancy, no increased risk of miscarriage or stillbirth, and no disruption to future menstrual cycles beyond the short term. A separate review of 47 studies reached the same conclusion. Three additional systematic reviews looking specifically at levonorgestrel-containing contraceptives found that conception rates after use were the same as those expected in the general population, regardless of how long or how often the medication was used.
How Plan B Works in Your Body
Plan B contains a single high dose of levonorgestrel, a synthetic hormone also found in many daily birth control pills. It works by delaying or stopping the release of an egg from the ovary. If ovulation hasn’t happened yet, Plan B prevents it from happening during the window when sperm could still be viable. The FDA has confirmed that Plan B has no direct effect on fertilization or implantation.
This is important context for the infertility question. Plan B doesn’t destroy eggs, scar your uterus, or alter your reproductive anatomy. It temporarily pauses one ovulation cycle. Once the hormone clears your system, your normal cycle resumes.
Side Effects of Repeated Use
While Plan B won’t make you infertile, taking it frequently does come with short-term side effects that can feel alarming. The most common is menstrual irregularity. Your next period may come earlier or later than expected, sometimes by a week or more. Bleeding can be heavier or lighter than usual. These changes are more likely if you’ve used Plan B more than once in the same menstrual cycle.
The WHO acknowledges that frequent use “can result in increased side-effects, such as menstrual irregularities,” but adds that “repeated use poses no known health risks.” A 2014 systematic review of 22 studies on people who used emergency contraception as their primary method of birth control confirmed that menstrual irregularities were the most common complaint. No serious health consequences were identified.
These cycle disruptions are temporary. They resolve on their own once you stop taking the medication, and they don’t signal any underlying damage to your reproductive system.
Why It’s Not Recommended as Regular Birth Control
If Plan B is safe to take repeatedly, you might wonder why doctors don’t suggest using it as your main contraceptive. Two reasons: it’s less effective, and it’s less predictable.
Plan B pills are 81% to 94% effective at preventing pregnancy, depending on how quickly you take them after unprotected sex. That’s significantly lower than daily oral contraceptives (which are over 99% effective with perfect use) or an IUD (99% effective). Relying on Plan B as your go-to method means accepting a meaningfully higher chance of unintended pregnancy compared to regular contraception.
The American College of Obstetricians and Gynecologists confirms that emergency contraception “may be used more than once, even within the same menstrual cycle.” But they recommend it as a backup, not a first-line strategy, simply because better options exist for ongoing pregnancy prevention.
Weight Can Affect How Well It Works
One factor worth knowing about is body weight. Research from Oregon Health & Science University found that people with a BMI of 30 or higher experienced Plan B failure four times as often as those with a BMI under 25. Blood levels of levonorgestrel were 50% lower in higher-BMI individuals after a standard dose, meaning the drug may never reach the concentration needed to block ovulation. Doubling the dose did not solve this problem.
If your BMI is 30 or above, a copper IUD placed within five days of unprotected sex is the most effective emergency contraception option, at 99% effectiveness regardless of weight. Another pill-based option, which uses a different active ingredient called ulipristal acetate, maintains better effectiveness at higher body weights than levonorgestrel, though it still becomes less reliable at very high BMIs.
The Bottom Line on Fertility
No study has ever identified a threshold at which Plan B causes infertility. The hormone it contains is the same one used in daily birth control pills and hormonal IUDs, just in a larger single dose. Long-term research on levonorgestrel across all its forms consistently shows no impairment of future fertility, even after years of use. Your ability to get pregnant returns as soon as the drug leaves your system, which happens within days.