How Effective Is Plan B? Emergency Contraception (EC) Explained

The short answer: emergency contraception is very effective, especially if you take it as soon as possible after sex. 

If you’re here because you had unprotected sex and want a clear answer, here it is. 

Emergency contraception, including Plan B and other options, can lower your chance of pregnancy. Timing matters most. The sooner you take it, the better it works.

Plan B and other emergency contraception pills that use levonorgestrel work best within 3 days (72 hours) after sex. They can still be used up to 5 days later, but they become less effective the longer you wait.

What is Plan B?

Plan B is a brand name for one type of emergency contraception, often called the morning-after pill. The same active ingredient, levonorgestrel, is also available in many generic options that work just as well.

Emergency contraception is medication you take after sex to help prevent pregnancy before it starts. Plan B is one option, but it is not the only one. Generic versions contain the same medication and are often more affordable and easier to access. Many health centers, including carafem, offer generic emergency contraception that is often more affordable and sometimes available at low or no cost.

Plan B is a form of emergency contraception. It is not the abortion pill.

People may use emergency contraception if they:

• Had sex without birth control

• Had a condom break or slip

• Missed birth control pills or started a pack late

• Were pressured or forced to have sex

Levonorgestrel emergency contraception is available as a single pill and can be purchased over the counter without a prescription. Another option, called ella (ulipristal acetate), requires a prescription. It may be a better option for people who weigh more, and it can be used up to 5 days after sex.

How does Plan B work?

Emergency contraception that uses levonorgestrel, including Plan B and generic options, works mainly by delaying ovulation. If no egg is released, sperm cannot fertilize it, and pregnancy cannot begin. If ovulation has already happened, Plan B and similar pills may not work as well.

Levonorgestrel emergency contraception does not affect an existing pregnancy.

Emergency contraception helps prevent pregnancy. It does not end one. If you already have a positive pregnancy test, this is not the medication you need.

How effective is Plan B?

Plan B can lower your chance of pregnancy by about 75% if taken within 3 days (72 hours) after sex. It works best the sooner you take it and becomes less effective over time.

Plan B is effective, but it is not 100%.

It works best when taken within 3 days (72 hours) after sex. It can still help up to 5 days later, but it becomes less effective the longer you wait.

Here’s a simple way to think about it:

• Within 3 days: best chance of working

• Up to 5 days: may still help, but works less well

• After ovulation: may not work 

Because ovulation is hard to predict, it’s usually worth taking emergency contraception as soon as possible. Even if you think there is a chance you may have ovulated, taking it will cause no harm, and it cannot work if you don’t take it.

Does weight affect how well Plan B works?

It can.

Plan B (levonorgestrel emergency contraception) may be less effective for people at higher body weights, though it may still work. It just may not work as well for some people.

Because of that, the best option can depend on both timing and your body.

If you weigh more or aren’t sure what to use:

• You can still take Plan B, especially if it’s your fastest option

• Another pill (ella) may work better and stays effective for up to 5 days

• An IUD is the most effective option and works regardless of weight

If you’re considering options like ella or an IUD, or aren’t sure what’s best for you, a clinician can help you decide based on your timing, needs, and preferences. The copper IUD is the most commonly used option for emergency contraception, but some hormonal IUDs may also work if placed within 5 days.

If you’re worried you may have already ovulated:

• Don’t avoid taking it just because you think you might have ovulated

• Ovulation is hard to predict

• If it hasn’t happened yet, emergency contraception can still work

• If you’re unsure, it’s still worth taking it rather than waiting

If you’re deciding in the moment:

• Take something as soon as possible

• Don’t wait to figure everything out

• If Plan B is what you have access to, it’s okay to take it

How do I take Plan B?

Plan B is simple to use. It is usually one pill taken as soon as possible after unprotected sex. It can be taken with or without food. Generic versions use the same medication and work the same way.

A few important things to know:

• It works best within 3 days

• If you vomit within 2 hours of taking it, you may need another dose

• It is safe to take while breastfeeding

How much does Plan B cost?

The cost of Plan B can vary depending on where you get it.

Brand-name Plan B often costs around $40 to $50. Generic versions contain the same active ingredient (levonorgestrel) and work the same way, but often cost less and may be easier to find.

Some insurance plans may cover emergency contraception, especially with a prescription.

If cost is a concern or you’re not sure which option to choose, a clinician (including at carafem) can help you find emergency contraception that fits your needs.

What if Plan B does not work?

It’s important to know that Plan B, or any levonorgestrel emergency contraception, will not harm an existing pregnancy. If you take it and later find out you’re pregnant, it will not affect the pregnancy.

If you take a pregnancy test and it is positive after taking Plan B, you still have options, and you deserve clear, supportive information to help you decide what’s right for you. 

You don’t have to figure this out on your own.

Plan B questions, answered

Do I need a prescription for Plan B?

No. Plan B and generic emergency contraception (levonorgestrel) are available over the counter and can be purchased at pharmacies, grocery stores, and many health centers without a prescription or age restriction. Ella does require a prescription.

What are the most common side effects of Plan B?

Most people tolerate emergency contraception well. Possible side effects of the medication can include nausea, fatigue, headache, breast tenderness, mild cramping, or irregular bleeding. These usually go away within a day or two.

Is Plan B the same as the abortion pill?

No. They’re different medications used at different times.

Emergency contraception is taken after sex to help prevent pregnancy. It works mainly by delaying ovulation. Abortion pills are used after a pregnancy has started to safely end an early pregnancy.

Can Plan B delay your period?

Yes. Your next period may come a little earlier or a little later than expected. Some people also notice spotting or a period that is heavier or lighter than usual. This is common and usually settles by your next cycle.

Does taking Plan B make you bleed or cramp?

It can. Some people notice spotting light bleeding or mild cramping after taking it. This does not always mean your period has started. If you have very heavy bleeding, severe pain, or symptoms that feel concerning, it is a good idea to check in with a clinician.

Can you take Plan B while using birth control?

Yes. Emergency contraception can be used if something goes wrong with your birth control, like missed pills, starting a pack late, or a condom breaking. 

Levonorgestrel (Plan B and generics) won’t interfere with your regular hormonal birth control, so you can keep taking your birth control as normal. 

Ella (ulipristal acetate) is another option, but it works a little differently. If you take it, you’ll need to wait 5 days before restarting your birth control pills, since starting or restarting them too soon can make Ella less effective. 

Either way, emergency contraception can help lower your chance of pregnancy if you’ve had unprotected sex.

Can Plan B make you infertile?

No. Emergency contraception does not affect long-term fertility or your future ability to get pregnant. You can also take it more than once if needed without impacting your future fertility.

Is there a maximum number of times I can take emergency contraception?

There is no set limit on how many times you can take emergency contraception. It can be used more than once, even within the same cycle if needed. Recommendations may vary slightly depending on the type you use.

• Levonorgestrel (Plan B and generics): can be used multiple times, even in the same cycle

• Ella: can be used again, but repeated use in the same cycle isn’t well studied

If you need emergency contraception again, it’s still worth talking to a clinician who can help you choose the best option.

Can you drink alcohol after taking Plan B?

Yes. There is no known interaction between alcohol and emergency contraception. 

These medications can sometimes cause nausea, and alcohol may make nausea worse for some people.

If you vomit within about two hours of taking it, the medication may not work as well. If that happens, check in with a clinician or pharmacist about what to do next.

Can I keep emergency contraception on hand? And what is its shelf life?

Yes. Many people choose to keep emergency contraception at home so it is available if they need it. Because timing matters, having it on hand can make it easier to take it as soon as possible after unprotected sex.

Medications do expire. Most packages have a shelf life of about two years, but you should always check the expiration date on the box before using it. If it has expired, it is best to replace it with a new one.

Store it at room temperature and avoid extreme heat or cold, which may affect how well it works.

Can emergency contraception make my period late? How do I know if it worked? 

Your period might not come exactly when you expect. That’s normal after taking emergency contraception.

The clearest sign it worked is that you get your period.

If your period hasn’t come within about a week of when you expected it, take a pregnancy test. You can also test about 3 weeks (21 days)  after unprotected sex for the most reliable result.

You’ve got options. We’ve got you.

Whether you’re considering a pill like Plan B or Ella, or an IUD, you don’t have to figure it out on your own. If you want help choosing what’s right for you, you can get care and see your options on our website or call 1-855-SAY-CARA.