Levonorgestrel Emergency Contraception: Plan B

Medically Reviewed by Zilpah Sheikh, MD on July 11, 2024
Written by Annie Stuart, Kristin Mitchell
6 min read

Plan B, also called the morning-after pill, is an emergency contraceptive pill taken after unprotected sex to prevent pregnancy. You don't, however, have to wait until the morning after sex to take it. 

It contains the hormone levonorgestrel, which is more effective the sooner you take it. 

Plan B is a one-dose regimen: You take one pill. The pill contains 1.5 milligrams of levonorgestrel, which is used in lower doses in many birth control pills.

Some brand names of emergency contraception that contain levonorgestrel are EContra EZ, My Way, Next Choice One Dose, Plan B One-Step, Preventeza, Take Action, Fallback Solo, and Opcicon One-Step.

You can buy Plan B without a prescription, however it’s not for routine contraceptive use. Also, it doesn’t protect you against sexually transmitted infections, including HIV.

Depending on where you are in your cycle, levonorgestrel helps prevent pregnancy after unprotected sex. It may prevent or delay ovulation.

The drug works by stopping the release of an egg from your ovary. It may prevent sperm from fertilizing the egg.

If fertilization does happen, it may prevent the fertilized egg from attaching to the womb. If the fertilized egg is implanted before you take levonorgestrel, the drug won’t work and pregnancy will proceed.

Does Plan B One-Step have a weight limit?

Although there is no specific weight limit, the medication may not be as effective at preventing pregnancy if you have obesity.

If you take it as directed within 72 hours after you've had unprotected sex, levonorgestrel can reduce your risk of pregnancy by up to 89%. If you take it within 24 hours, it works even better.

But you should know that levonorgestrel isn’t as effective as regular contraception. So don't use it as a form of birth control. And it doesn’t protect you against sexually transmitted diseases. Think of it as a backup – it’s not for routine use. That's why it's called Plan B. 

You can buy Plan B One-Step over the counter at drugstores without a prescription or proof of age.

The pill is taken in one tablet which contains 1.5 milligrams of levonorgestrel (vs. the Plan B pill, which is taken as two doses of 0.75 milligram). Although it can be taken without food or water, eating and/or drinking with the pill may help to lessen nausea.

 Plan B One-Step works best when it's taken as soon as possible, within 72 hours of birth control failure or unprotected sex. 

 

 

 

You can take Plan B One-Step if:

  • You didn't use any birth control.
  • The condom came off or broke.
  • Your diaphragm slipped out of place.
  • You missed at least two or three active birth control pills in a row.
  • You forgot to insert your ring or apply your patch.
  • The pull-out method wasn't effective.
  • You have another reason to think your birth control might not have worked.
  • You were forced to have unprotected sex.

Remember: Plan B will not protect you from getting pregnant if you have unprotected sex after taking it. To protect you against getting pregnant, you need to take it right after you have unprotected sex and use a form of contraception when you have sex.

Don’t take levonorgestrel if:

  • You know you’re pregnant or suspect you might be.
  • You have a history of allergy or are very sensitive to its ingredients.
  • You have a history of recent abnormal vaginal bleeding that your doctor hasn’t checked.

Many women have taken emergency contraception without serious complications. But it's a good idea to ask your doctor about possible interactions with other medications.

Levonorgestrel is considered safe for most women. You shouldn’t take it if you’re pregnant because it will not end your pregnancy.

Potential side effects of levonorgestrel include:

If you vomit within 2 hours after taking the drug, call a health care professional to find out if you should repeat the dose.

With levonorgestrel, you may also have some unexpected bleeding. It should go away by the time of your next period. 

It’s possible that levonorgestrel may cause your next period to be heavier or lighter than usual, and it may come earlier or later than is normal for you. If you don't get your period within 3 weeks, you should take a pregnancy test to confirm whether you're pregnant or not.

Read more on emergency contraception side effects.

The Plan B One-Step pill and emergency contraception in general are considered effective and safe for preventing unwanted pregnancy after unprotected sex. Also, the pill doesn't affect your ability to get pregnant in the future.

It's important to remember that it's not to be used as a routine birth control method.

No. RU-486, sold as Mifeprex, is a prescription drug for medical abortion. Mifeprex works after you’re already pregnant, while Plan B won't work then. Doctors prescribe Plan B as emergency contraception, not as an abortion pill.

The Plan B One-Step pill, also known as the morning-after pill, is a type of emergency contraception taken after unprotected sex or missed birth control to prevent pregnancy.

It contains the hormone levonorgestrel and is a one-dose regimen that includes 1.5 milligrams of levonorgestrel. 

Although there are possible side effects, including nausea and vomiting, dizziness, and changes to your menstrual cycle, the pill is generally considered safe and effective in preventing pregnancy. It works better the sooner you take it, being most effective for up to 72 hours after unprotected sex.

After taking the pill, talk to your doctor if you have continued spotting or irregular bleeding, heavy bleeding, or pain in your stomach. These symptoms may be sign of a miscarriage or ectopic pregnancy (where the fertilized egg forms outside of the womb).

What is Plan B used for? Plan B is used to prevent pregnancy in cases of missed birth control and unprotected sex.

Is Plan B 100% safe? The Plan B One-Step pill and emergency contraception in general is considered effective and safe for preventing unwanted pregnancy after unprotected sex. Also, the pill doesn't affect your ability to get pregnant in the future.

What happens after taking a pill? Many women have taken emergency contraception without serious complications. Potential side effects of levonorgestrel include nausea or vomiting, belly pain, tiredness, headache, changes to your menstrual cycle, dizziness, and breast sensitivity.

Am I safe if I take Plan B? The pill is considered safe and effective when used correctly, but you shouldn't take it if you're allergic to what's in the pill or are taking certain medications. Also, it may not work as well if you aren't at a healthy weight or have obesity.

Can I be pregnant after taking the morning-after pill? It's possible to be pregnant after taking the pill if your pregnancy has implanted (if a fertilized egg has already attached to the uterus). Keep in mind that the pill doesn't work as well as other forms of birth control, and it's possible for it to fail even if you use it correctly.

Is one morning-after pill enough to prevent pregnancy? The Plan B One-Step pill is up to 89% effective in preventing pregnancy for up to 72 hours. The effectiveness depends on how quickly the pill is taken after failure of birth control or unprotected sex.