Plan B emergency contraception was first approved by the U.S. Food and Drug Administration (FDA) in 1999. It arrived as a dedicated product designed to prevent pregnancy after unprotected sex or contraceptive failure, offering a second chance when regular birth control was not used or did not work. Before 1999, people used higher doses of regular birth control pills off-label, but Plan B was the first pill made specifically for this purpose.
What Exactly Is Plan B and How Does It Work?
Plan B is a single active ingredient called levonorgestrel. It is a synthetic hormone that has been used in birth control pills for decades. The difference is the dose — Plan B contains a higher amount taken in one or two pills.
The pill works by stopping or delaying the release of an egg from the ovary. If no egg is released, sperm cannot fertilize one. It may also thicken cervical mucus to block sperm from reaching an egg. Research published in the journal Contraception has confirmed that Plan B does not work after a fertilized egg has implanted in the uterus. It is not an abortion pill.
Plan B is most effective when taken within 72 hours (three days) after unprotected sex. The sooner you take it, the better it works. Studies show it reduces the risk of pregnancy by 75 to 89 percent when taken correctly.
When Was Plan B Invented and Who Developed It?
The original Plan B pill was developed by the Women’s Capital Corporation, a company focused on reproductive health. The FDA approved it for prescription-only use in July 1999. At that time, you needed to see a doctor to get it.
The active ingredient — levonorgestrel — had been used in regular birth control pills since the 1970s. What made Plan B new was the packaging and dosing designed specifically for emergency use. Before 1999, doctors sometimes prescribed a “Yuzpe regimen” using multiple regular birth control pills taken in two doses. That method was less convenient and caused more nausea.
In 2006, the FDA approved Plan B for over-the-counter sale to people aged 18 and older. In 2013, that age restriction was removed. As of 2026, Plan B and its generic versions are available without a prescription to anyone of any age at most pharmacies.
Does Plan B Work for Everyone?
No contraceptive works perfectly for everyone. Plan B is less effective for people with a higher body mass index (BMI). Research published in Contraception in 2011 found that women with a BMI over 25 had a higher pregnancy rate after taking levonorgestrel emergency contraception. For women with a BMI over 30, the failure rate was significantly higher.
This does not mean Plan B is useless for these individuals. It means it is less reliable. The alternative is ella (ulipristal acetate), a different emergency contraceptive that the FDA approved in 2010. Studies suggest ella works better than Plan B across all body weights and remains effective for up to five days.
Plan B also does not protect against sexually transmitted infections (STIs). Only condoms reduce STI risk.
| Product | Active Ingredient | Window | Prescription Needed? |
|---|---|---|---|
| Plan B (and generics) | Levonorgestrel | Up to 3 days | No |
| Ella | Ulipristal acetate | Up to 5 days | Yes |
| Copper IUD (Paragard) | Copper | Up to 5 days | Inserted by clinician |
What Are the Side Effects of Plan B?
Most people tolerate Plan B well. The most common side effects include nausea, headache, dizziness, breast tenderness, and fatigue. Some people experience irregular bleeding or spotting in the days after taking it. Your next period may come earlier or later than expected.
Vomiting is less common but can happen. If you vomit within two hours of taking Plan B, the dose may not be fully absorbed. In that case, you should take another dose or contact a healthcare provider.
These side effects usually resolve within 24 hours. They are not dangerous. Plan B has been studied extensively for over 25 years, and the FDA has consistently confirmed its safety profile. Serious complications are extremely rare.
What Are Common Misconceptions About Plan B?
One frequent myth is that Plan B causes infertility. This is false. The CDC and the American College of Obstetricians and Gynecologists (ACOG) both state that emergency contraception does not affect long-term fertility. Taking Plan B multiple times in one cycle will not prevent you from getting pregnant in the future.
Another myth is that Plan B is the same as the abortion pill mifepristone. It is not. Plan B prevents ovulation or fertilization. It does not end an established pregnancy. The confusion often comes from the term “morning-after pill,” which sounds similar to “abortion pill” but refers to a completely different drug and mechanism.
A third misconception is that you need to take Plan B immediately after sex for it to work. While taking it sooner is better, you still have a full 72-hour window. The idea that it is useless after 24 hours is incorrect. Studies show effectiveness declines gradually over the three-day period but does not suddenly drop off.
What Should You Avoid When Using Plan B?
Avoid taking Plan B with certain medications that can reduce its effectiveness. These include some antiseizure drugs, the antibiotic rifampin, the antifungal griseofulvin, and St. John’s wort, an herbal supplement used for depression. If you take any of these regularly, ella or a copper IUD may be better options.
Do not rely on Plan B as your primary birth control method. It is meant for emergencies only. Using it repeatedly in one menstrual cycle is not harmful, but it is less effective than regular contraception like the pill, patch, ring, IUD, or implant. The failure rate per use is higher than most ongoing methods.
Avoid assuming Plan B worked if your next period is late. No emergency contraceptive is 100 percent effective. If your period is more than seven days late, take a pregnancy test. If the test is positive, see a healthcare provider.
Do not take Plan B if you are already pregnant. It will not harm a developing fetus, but it will not end a pregnancy. There is no reason to take it if you know you are pregnant.
Frequently Asked Questions
Can you buy Plan B at age 16?
Yes. Plan B is available over the counter to people of any age. No prescription or ID is required.
Does Plan B expire?
Yes. Check the expiration date on the package. An expired pill may be less effective, so do not use it past that date.
Can Plan B cause a false positive pregnancy test?
No. Plan B does not contain hCG, the hormone that pregnancy tests detect. It will not cause a false positive.
How many times can you take Plan B in one month?
You can take it more than once in a cycle if needed. It is safe but not ideal as a regular method because it is less effective than ongoing contraception.
