There is no medical limit on how many times you can take Plan B. You can use it more than once in the same menstrual cycle, and taking it repeatedly poses no known health risks. That said, it’s a less effective and more expensive option than regular birth control, so relying on it as your go-to method isn’t ideal for practical reasons.
No Set Limit, but More Side Effects
Plan B is labeled for single use, but that’s a packaging distinction, not a safety ceiling. The European Consortium for Emergency Contraception reviewed the evidence and confirmed that taking emergency contraceptive pills more than once, even within the same cycle, does not pose known health risks. The World Health Organization echoes this, noting that repeated use carries no identified dangers beyond an increase in side effects.
Those side effects are manageable but annoying. A single dose can cause nausea, fatigue, headache, and breast tenderness. The more often you take it, the more frequently you’ll deal with these. The biggest nuisance is what it does to your cycle: spotting between periods, periods arriving early or late, and flow that’s heavier or lighter than normal. If you’re taking Plan B multiple times in a short window, expect your cycle to be unpredictable for a while.
It Won’t Hurt Your Future Fertility
This is one of the most common fears, and the evidence is reassuring. A 2022 review in the journal Contraception concluded that repeated use is unlikely to affect future fertility. Three separate systematic reviews of the hormone in Plan B found no detrimental effect on time to pregnancy, regardless of how long or how often it was used. Conception rates after stopping were similar to those in the general population. There’s also no evidence that exposure harms fetal development, increases miscarriage risk, or causes stillbirth.
Effectiveness Drops Fast With Each Hour
Plan B works best the sooner you take it. Within the first 24 hours, it’s roughly 94% effective at preventing pregnancy. By 72 hours, that number falls to about 58%. After 72 hours, it’s not recommended at all. So while you can take it as many times as you need to, timing matters far more than frequency.
Limited evidence suggests that taking Plan B multiple times doesn’t make it less effective on any individual dose. Each use appears to work independently, so a second dose in the same cycle should perform similarly to the first, assuming you take it promptly.
Weight Can Change How Well It Works
This is something many people don’t realize. Plan B starts losing effectiveness at around 155 pounds (70 kg) and may provide essentially no protection at 176 pounds (80 kg) or above. The reason is straightforward: at higher body weights, blood levels of the active hormone reach only about half the concentration seen in lighter individuals. For people with a BMI of 30 or higher, the risk of pregnancy on Plan B is more than four times greater compared to those with a BMI under 25.
If this applies to you, a copper IUD inserted within five days of unprotected sex is the most effective emergency option regardless of weight. Another pill option, sold under the brand name ella, maintains better efficacy at higher weights, though it does require a prescription.
Why Regular Birth Control Makes More Sense
Plan B costs around $30 to $50 per dose at most pharmacies. If you’re using it a few times a year, that adds up quickly compared to daily birth control pills, which are often free or low-cost with insurance. Beyond cost, regular contraception is simply more reliable. The pill, patch, ring, IUD, and implant all have higher effectiveness rates than emergency contraception when used consistently.
If you’ve just taken Plan B and want to start a regular method, you don’t have to wait. The CDC confirms you can begin any standard contraceptive method immediately after taking it. The one caveat: use condoms or abstain for the first seven days while your new method takes effect. And if your period doesn’t arrive within three weeks, take a pregnancy test to be sure.
Plan B is a backup, and it’s a good one to have available. But if you’re reaching for it regularly, that’s a signal to explore options that give you better protection with fewer disruptions to your cycle and your wallet.