After taking Plan B, the most important thing to know is that the pill is already working. There’s no additional step you need to take right now to make it more effective. What comes next is managing any side effects, knowing when to expect your period, and understanding when to take a pregnancy test if your period doesn’t arrive on time.
What Plan B Is Doing in Your Body
Plan B contains a hormone called levonorgestrel that works by delaying or preventing your ovary from releasing an egg. If there’s no egg available, sperm can’t fertilize anything. It does not end a pregnancy that has already started, and it cannot harm a developing embryo. Think of it as hitting pause on ovulation long enough for sperm (which survive only a few days) to die off before an egg appears.
Taking an extra dose won’t make it work better. If you’ve already taken the recommended dose, a second pill on the same day or the next day adds nothing.
Side Effects You Might Notice
Most people experience mild side effects, if any. The most common ones include nausea, headache, fatigue, dizziness, breast tenderness, and cramping or abdominal pain. Some light spotting between periods is also normal. These symptoms typically resolve within a day or two.
If you vomit within two hours of taking the pill, it may not have been fully absorbed and you may need another dose. Nausea without vomiting doesn’t affect how well the pill works.
What to Expect With Your Next Period
Plan B commonly shifts the timing of your next period. It might come a few days early, or it might be late. The flow can also look different from what you’re used to: lighter, heavier, or with more spotting beforehand. All of this is a normal response to the extra dose of hormone and doesn’t mean the pill failed or that something is wrong.
If your period is more than a week late, that’s when you should take a pregnancy test. The general guideline is to test at least 21 days after the unprotected sex that prompted you to take Plan B. Testing earlier than that can produce a false negative because pregnancy hormone levels may not be high enough to detect yet.
Body Weight and Effectiveness
Research has found that Plan B becomes less effective for people with a BMI above 26. If that applies to you, the pill may still offer some protection, but the reduction in effectiveness is significant enough to be worth knowing about. A copper IUD inserted within five days of unprotected sex is the most effective emergency contraception regardless of weight, and some clinics can place one on short notice.
Restarting Your Regular Birth Control
If you’re on hormonal birth control and needed Plan B because of a missed pill or another error, you can resume your regular method immediately. You don’t need to wait for your next period, and if you’re on the pill, you don’t need to start a new pack. Just pick up where you left off. Patch users should start with a fresh patch, and ring users should follow the instructions for late replacement.
The key detail: use a backup method (condoms, or avoid sex) for the first seven days after restarting. Your regular birth control needs that time to become fully effective again.
If you took ella (ulipristal acetate) instead of Plan B, the timeline is different. You should wait five full days before restarting any birth control that contains hormones, because the two can interfere with each other. You also should not take Plan B and ella within five days of each other, as they can cancel each other out.
If You Need Emergency Contraception Again
There’s no medical limit to how many times you can take Plan B, even within the same menstrual cycle. Frequent use of levonorgestrel-based emergency contraception isn’t associated with long-term side effects or complications. That said, it’s less effective than using a regular method of birth control consistently, so if you’re finding yourself reaching for Plan B often, it may be worth exploring a method that doesn’t depend on remembering a daily pill, like an IUD or implant.
Symptoms That Need Attention
Mild cramping and nausea are expected. Severe abdominal pain, especially pain concentrated on one side, is not. This can be a sign of an ectopic pregnancy, where a fertilized egg implants outside the uterus. Ectopic pregnancies are rare but serious, and they require prompt medical care. If you develop intense, sharp stomach pain in the weeks after taking Plan B, get evaluated right away.
Heavy bleeding that soaks through a pad in an hour or less, or bleeding that doesn’t stop after several days, also warrants a call to a healthcare provider. Light spotting, by contrast, is completely normal and usually resolves on its own.
The Waiting Period, Practically Speaking
The hardest part for most people is simply the waiting. You’ve taken the pill, you can’t do anything else to change its effectiveness, and now you have to wait for your period to confirm it worked. During that time, a few practical things help. Track the date you took Plan B and the date of the unprotected sex so you can accurately time a pregnancy test if needed. Use a backup method for any sex in the meantime, since Plan B only covers the single episode that prompted you to take it. And try not to read too much into every cramp or twinge. The side effects of the pill itself can mimic early pregnancy symptoms, which creates unnecessary anxiety.
If your period arrives, even if it’s lighter or slightly off-schedule, that’s your confirmation. If it doesn’t arrive within a week of when you expected it, a standard home pregnancy test taken at least 21 days after unprotected sex will give you a reliable answer.