You’re staring at the box. Your heart is probably racing a little bit, and you’re scrolling through a sea of medical jargon trying to find a straight answer to one specific question: when do i take plan b?
The short answer? Right now.
If you just had an "oops" moment—the condom broke, you missed a few pills, or things just got carried away—the clock is officially ticking. It’s not about waiting for a specific time of day or waiting to see if you feel "different." It’s about the biological race between a pill and a process called ovulation.
The 72-Hour Window Is Real (But Kind Of Misleading)
Most people think they have a leisurely three days to figure things out. Technically, the FDA labels Plan B One-Step (and its generic cousins like Take Action or My Way) for use up to 72 hours after unprotected sex.
But here’s the thing.
Plan B is significantly more effective the sooner you take it. If you take it within 24 hours, it’s about 95% effective. By the time you hit the 48-to-72-hour mark, that efficacy drops to roughly 89% or lower. It’s not that the pill suddenly expires at hour 73; it’s that every hour you wait gives your body a chance to release an egg. Once that egg is out, Plan B is basically just a very expensive vitamin. It won't do anything.
How the Science Actually Works
Plan B is essentially a high dose of levonorgestrel. That’s a synthetic version of the hormone progestin, which is already used in many birth control pills. It works by sending a signal to your brain to "hold the phone" on ovulation. It delays the release of an egg from the ovary.
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If there is no egg, the sperm (which can live inside you for up to five days, by the way) has nothing to fertilize.
Contrary to some persistent myths and political rhetoric, Plan B is not an abortion pill. It doesn't end an existing pregnancy. If an egg has already been fertilized and implanted, the levonorgestrel won't disturb it. This is why timing is the only thing that matters. If you’ve already ovulated, taking the pill might not help you at all.
What About the "Five Day" Rule?
You might have heard about a five-day window. This usually refers to ella (ulipristal acetate), which is a different kind of emergency contraception that requires a prescription. Ella stays effective at the same rate for all 120 hours. There’s also the copper IUD, which is the most effective emergency contraception available, but that requires an appointment and an insertion by a professional.
Weight Limits and Efficacy: The Elephant in the Room
This is the part that doctors often gloss over, but it’s vital. Research, including studies cited by the Association of Reproductive Health Professionals, suggests that Plan B might be less effective for people who weigh over 165 pounds or have a BMI over 25.
It’s not a "yes or no" situation where it just stops working, but the concentration of the hormone in the bloodstream may be lower in people with higher body mass. If you fall into this category, you aren't out of luck, but you might want to talk to a provider about ella or a copper IUD, which don't have these same weight-related efficacy drops.
Side Effects: Expect the Weirdness
So, you took it. Now what?
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Honestly, you’re probably going to feel a bit "off." Because Plan B is a massive hormone hit, it messes with your cycle. Your next period might be a week early, or it might be a week late. It might be much heavier than usual, or just weird spotting.
Common stuff includes:
- Nausea (the big one)
- Lower abdominal cramping
- Fatigue (feeling like you need a 3-hour nap)
- Breast tenderness
- Dizziness
If you vomit within two hours of taking the pill, stop. The medication likely didn't get absorbed. You’ll need to call a pharmacist or doctor because you probably need a second dose.
When Do I Take Plan B if I'm Already on the Pill?
This is a common point of confusion. If you realized you missed two days of your regular birth control and had sex, you should take Plan B as soon as possible. However, you should also resume your regular birth control pills immediately to stay on track for the rest of the month.
Just keep in mind that you'll need to use a backup method (like condoms) for the next seven days. The hormones in the emergency pill and your regular pill are playing on the same team, but the "oops" means your baseline protection was compromised.
The Myth of "Too Much" Plan B
There’s a weird rumor that taking Plan B too many times will make you infertile.
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It’s false.
There is no evidence that emergency contraception has long-term effects on your ability to get pregnant later. That said, it’s called "emergency" for a reason. It’s not meant to be your primary birth control because it's less effective than the daily pill, the patch, or an IUD. It’s also way more expensive. Buying a $50 pill every time you have sex is a quick way to go broke when a monthly prescription is often free under many insurance plans.
Tracking Your Results
Taking the pill isn't the end of the story. You have to follow up. Since Plan B shifts your cycle, you can't rely on your "usual" period date to know if you're safe.
Experts generally recommend taking a pregnancy test about three weeks after taking Plan B. Taking one the next day won't tell you anything—it takes time for the hCG hormone to build up enough to trigger a positive result. If your period is more than a week late, pee on a stick.
A Note on Privacy and Access
In the current legal climate, many people are nervous. Plan B is currently legal in all 50 states and is available over the counter without a prescription or ID, regardless of age. You don't have to talk to a pharmacist; you can usually just grab it off the shelf at a CVS, Walgreens, or Target.
If you’re worried about the cost, organizations like Planned Parenthood or local health clinics often offer it on a sliding scale or even for free.
Your Action Plan
Don't overthink this. If you are questioning whether you should take it, the answer is almost certainly yes.
- Check the time. If it's been less than 72 hours, go to the pharmacy immediately. If it's been between 72 and 120 hours, call a doctor or use a telehealth app (like Nurx or Planned Parenthood Direct) to get a prescription for ella.
- Eat a small snack. Taking Plan B on a totally empty stomach is a recipe for nausea. A few crackers can help keep the pill down.
- Reschedule your life for 24 hours. You might feel fine, or you might feel like you have the flu. Give yourself grace to rest.
- Mark your calendar. Set a reminder for 21 days from today to take a pregnancy test.
- Evaluate your "Plan A." Once the dust settles, think about whether your current birth control method is actually working for your lifestyle. If remembering a pill is too hard, maybe look into the Nexplanon arm implant or an IUD.
The window of opportunity is small, and your peace of mind is worth the trip to the store. Take it, breathe, and then move forward.