You take one Plan B pill, one time. The standard dose is a single 1.5 mg tablet, taken as soon as possible after unprotected sex. Taking extra pills does not make it more effective. There are some specific situations where a second pill applies, but for most people, one is all you need.
The Standard Dose Is One Pill
Plan B One-Step contains 1.5 mg of levonorgestrel in a single tablet. You take it as soon as you can, ideally within 72 hours (3 days) of unprotected sex. It works by delaying or preventing ovulation, so the sooner you take it, the better your chances. Effectiveness ranges from 81% to 90% depending on how quickly you act, and it drops further if you wait beyond 72 hours, though it can still be used up to 5 days after.
Some older packaging split this same dose into two 0.75 mg pills taken 12 hours apart. If you have that version, take both pills as directed. Either way, the total dose is the same: 1.5 mg of levonorgestrel.
Why Taking Extra Pills Won’t Help
Taking additional pills beyond the recommended dose does not increase your protection. Plan B works by flooding your system with enough synthetic hormone to block ovulation. Once that threshold is met, adding more of the same hormone doesn’t improve the outcome. It can, however, increase side effects like nausea.
The Exception: Vomiting After Taking It
If you vomit within 2 to 3 hours of swallowing the pill, your body may not have absorbed enough of the medication. In that case, you should take another dose as soon as possible. The CDC recommends considering an anti-nausea medication before the second dose to help keep it down. Outside of vomiting, there is no reason to repeat the dose.
What If You Weigh More Than 165 Pounds
This is where the question gets more nuanced. Some studies have found that Plan B is less effective in people who weigh over 165 pounds, with some research showing up to double the risk of pregnancy compared to someone at a lower weight. The data is mixed, though. Other studies have found no significant difference based on weight.
The pharmacology offers a partial explanation: blood levels of levonorgestrel after the standard 1.5 mg dose are measurably lower in people with obesity. Doubling the dose to 3 mg (two pills) can correct those blood levels. However, a 2022 study found that for people with a BMI over 30 and weight over 176 pounds, the doubled dose didn’t significantly reduce the risk of ovulation compared to the standard dose, particularly when taken close to the fertile window.
Medical guidance from the UK’s Faculty of Sexual and Reproductive Healthcare states that a clinician may offer a 3 mg dose (two pills) to someone weighing over 154 pounds or with a BMI over 26, but notes that a copper IUD is the preferred emergency contraception for this group because its effectiveness is not influenced by weight. A different pill called ella (ulipristal acetate) is another option that maintains about 94% effectiveness regardless of when it’s taken within a 5-day window, and it may be a better choice for people in higher weight ranges.
If you weigh over 165 pounds, Plan B is still worth taking. It remains better than not using any emergency contraception at all. But if you have time to see a provider, ask about alternatives that may work more reliably for your body.
Multiple Instances of Unprotected Sex
If you had unprotected sex on two separate occasions in the same cycle, each instance needs its own dose of Plan B. One pill does not provide ongoing protection. There is no limit to how many times you can take Plan B in a single menstrual cycle, and frequent use is not associated with long-term side effects or fertility problems.
That said, Plan B is less effective than regular contraception and costs more per use. If you’re reaching for it repeatedly, it’s a sign that a daily method, an IUD, or an implant would serve you better. Menstrual irregularity, including spotting, shorter cycles, or longer periods, is the most common side effect of repeated use.
After You Take It
Once you’ve taken Plan B, you can start or resume your regular birth control method right away. You’ll need to use condoms or abstain for 7 days while your regular method takes effect. Your next period may come earlier or later than expected, which is normal. If your period is more than a week late, take a pregnancy test.