It’s 2:00 AM, and you just realized the condom broke or you forgot your pill for the third day in a row. Panic sets in. You run to the pharmacy, pay the $50, and swallow that little white pill. Now what? You’re probably sitting there wondering what happens after you take Plan B, staring at your reflection and waiting for something—anything—to feel different.
The truth? Usually, nothing happens immediately. You don’t feel a "click" or a sudden shift in your soul. But inside, your endocrine system is basically hitting the panic button to stop an egg from meeting a sperm.
The immediate biological scramble
Plan B is just a massive dose of levonorgestrel, a synthetic hormone that’s been around for decades. It's the same stuff in many birth control pills, just at a much higher concentration. When people ask what happens after you take Plan B, they’re usually looking for a timeline.
Within about 30 minutes to two hours, the hormone levels in your bloodstream peak. This isn't a "medical abortion" pill like mifepristone; it doesn't end a pregnancy. Instead, it acts like a biological roadblock. If you haven't ovulated yet, the levonorgestrel signals your brain to stall. It tells the luteinizing hormone (LH) surge to pipe down, effectively delaying the release of an egg for a few days. Since sperm can live inside you for up to five days, delaying ovulation by even 48 hours is often enough to make sure the egg arrives late to a party where all the guests have already left (or died).
But here’s the kicker that most people miss: if you’ve already ovulated, Plan B is basically expensive candy. Research from the International Federation of Gynecology and Obstetrics (FIGO) and other major health bodies has shown that levonorgestrel doesn't really do much once the egg is out of the gate. It doesn't prevent a fertilized egg from implanting as effectively as we once thought. It’s a timing game.
The side effects nobody warns you about (or they over-hype)
You might feel fine. Seriously.
Many people expect to be doubled over in pain or vomiting, but a lot of users just feel a bit "off." Nausea is the big one, though. About 10% to 15% of people will feel like they need to throw up. If you actually do vomit within two hours of taking the pill, you're back to square one because your body hasn't absorbed the hormone yet. You'll need another dose.
Then there’s the fatigue. You might feel like you’ve been hit by a truck or just need an aggressive four-hour nap. Some people get dizzy. Others get breast tenderness that makes wearing a bra feel like a personal insult.
Spotting is the great deceiver
One of the most stressful things regarding what happens after you take Plan B is the "oops" bleeding. A few days after taking it, you might notice some spotting. This isn't your period. It’s just your uterine lining reacting to the sudden drop in hormones after that massive spike you just gave it. It’s annoying, it’s messy, and it makes you wonder if it’s "implantation bleeding." (Pro-tip: it's almost certainly just the Plan B).
Your next period will probably be weird
Expect your cycle to be a chaotic mess for a month or two. Because you messed with the timing of ovulation, your actual period might show up a week early or a week late. It might be heavier. It might be lighter.
This is where the anxiety peaks. If your period is late, you think you’re pregnant. If it’s early, you worry something is wrong. According to clinical trials by Teva Pharmaceuticals (the folks who make Plan B One-Step), the majority of women get their period within a week of the expected time. But "expected" is a loose term when you've just dropped a hormone bomb on your ovaries.
If your period is more than a week late, take a test. It’s the only way to know for sure.
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The weight limit controversy
We need to talk about the 165-pound "limit." It’s been a massive point of contention in health circles for years. Some studies suggest that levonorgestrel is less effective for people with a Body Mass Index (BMI) over 25 or who weigh more than 165 pounds.
The science is a bit muddy here. The FDA has maintained that the data is "conflicting and too limited to make a definitive conclusion," but many doctors, like those at Planned Parenthood, suggest that if you’re over that weight threshold, you might want to look at the copper IUD or Ella (ulipristal acetate). Ella requires a prescription, but it's more effective for a wider range of body types. Don't let this stop you from taking Plan B if it's your only option—it's still better than doing nothing—but it's worth knowing that its efficacy isn't a flat 100% across the board.
Mental health and the "Hormone Crash"
Why does no one talk about the mood swings? You’re flooding your body with progestin. For some, this triggers a downward spiral of anxiety or irritability that lasts a few days. It's a lot like PMDD on fast-forward. If you already struggle with depression or anxiety, you might notice a temporary dip. It’s not in your head; it’s in your blood chemistry.
What to do right now
If you just took it, breathe. The hardest part is over.
- Check the clock. Note the time you took it. If you barf in the next two hours, go buy another one.
- Eat something small. A little toast or some crackers can help settle the stomach and mitigate that nausea.
- Track the spotting. Start a note on your phone or use a cycle app. You’ll forget the dates in two weeks, and you’ll want them when you’re staring at a calendar wondering where your period is.
- Don't take a pregnancy test tomorrow. It won't work. Your body needs time to build up hCG if a pregnancy actually occurs. Wait at least three weeks after the "incident" to take a test for an accurate result.
- Get a backup plan. Plan B is for emergencies. It’s not as effective as regular birth control and it’s way more expensive. If you find yourself wondering what happens after you take Plan B more than once or twice a year, it might be time to chat with a provider about a LARC (Long-Acting Reversible Contraception) like an IUD or the arm implant.
The drug stays in your system for a while, but its "action" is short-lived. Once it has successfully delayed ovulation, its job is done. It doesn't protect you from any unprotected sex you have after taking the pill. If you have another mishap tomorrow, you’re looking at another dose.
Your body is resilient. It can handle a hormonal surge. Just be kind to yourself over the next week. Drink water, wear the comfy pants, and try not to spiral over a late period until you’ve actually hit the seven-day-late mark.