Plan B is designed as a single-dose treatment: one pill, taken as soon as possible after unprotected sex. Taking a second pill on the same day is not recommended and does not improve your chances of preventing pregnancy. The full effective dose is contained in that one tablet.
Why One Pill Is the Full Dose
Each Plan B tablet contains 1.5 mg of levonorgestrel, a synthetic hormone that works by delaying or preventing the release of an egg from the ovaries. If ovulation hasn’t happened yet, the drug can stop it. If ovulation has already occurred, the pill may not work, and taking a second one won’t change that. The medication does not end a pregnancy that has already begun.
The one scenario where a second pill is appropriate: if you vomit within two hours of taking the first one. In that case, your body likely didn’t absorb enough of the medication, and you may need another dose. Outside of that situation, doubling up provides no additional protection.
What Happens If You Take More Than One
Taking extra pills is unlikely to cause serious harm. Hormonal contraceptive overdoses are generally not life-threatening. But higher doses of levonorgestrel do increase side effects, including nausea, vomiting, headache, breast tenderness, heavy vaginal bleeding (sometimes appearing two to seven days later), drowsiness, and emotional changes. These side effects are the same ones you might experience from a single dose, just potentially more intense.
A systematic review published in BMJ Sexual & Reproductive Health examined repeated emergency contraceptive use within a single menstrual cycle. In one trial, participants used an average of four to seven pills per month over six and a half months. About 78% of adverse events were mild (headache, nausea, abdominal pain), roughly 20% were moderate, and the small number of severe events were judged unrelated to the medication itself. The overall finding: the body of evidence does not suggest major safety concerns with repeated use, though the data remains limited.
One notable finding, however, involved ectopic pregnancy. A case-control study found that women who used levonorgestrel multiple times in a single conception cycle had roughly 2.5 times the odds of an ectopic pregnancy compared to those who used it once. This doesn’t mean repeated use causes ectopic pregnancies, but it’s a signal worth paying attention to.
Timing Matters More Than Dose
The biggest factor in whether Plan B works is how quickly you take it. The pill is most effective within the first 24 hours and should be taken no later than 72 hours (three days) after unprotected sex. With every passing hour, effectiveness drops. If you’re worried because it’s been a while since you took it, the answer is not to take another pill. It’s to consider whether a more effective option is available.
When Plan B Might Not Be Enough
Plan B has a significant limitation tied to body weight. If you weigh more than 165 pounds, levonorgestrel-based pills may not work effectively. A prescription alternative called ella uses a different compound and remains more effective at higher body weights, though its efficacy also decreases above 195 pounds. Ella is also more effective than Plan B at every time point within the five-day window, not just for people at higher weights.
The most effective form of emergency contraception is a copper IUD, which can be placed up to five days after unprotected sex and reduces pregnancy risk by more than 99%. It also doubles as long-term birth control afterward.
Starting Regular Birth Control After Plan B
You can start or restart hormonal birth control immediately after taking Plan B. There’s no need to wait for your next period. If you were already on the pill and missed doses (which led to needing emergency contraception in the first place), you can resume your current pack right away. If you use a patch, apply a new one. The key detail: use a backup method like condoms for the first seven days after starting or restarting your regular contraception, since it takes about a week for hormonal methods to become fully effective again.