How Effective Is Plan B One-Step?

Plan B One-Step (levonorgestrel) is a widely used form of emergency contraception (EC) that can effectively decrease the chance of unintended pregnancy after unprotected sexual intercourse.

Plan B One-Step is most effective when used as soon as possible after unprotected sex, but it can still be effective for up to three days (sometimes up to five days) after unprotected sex or birth control failure.

Plan B One-Step is available over-the-counter (OTC) at pharmacies, family planning clinics, or health department clinics.

You do not need a prescription or identification to buy Plan B One-Step, and people of any age or gender may buy it.

This article will discuss Plan B One-Step, highlighting its efficacy, cost, side effects, and other important information.

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What Is Plan B One-Step?

Plan B One-Step is a brand-name, orally administered medication (taken by mouth) containing 1.5 milligrams (mg) of levonorgestrel, its active ingredient.

The ingredient levonorgestrel has been used in birth control pills for many years.

Plan B One-Step, however, is different from regular birth control pills in that it is taken after unprotected sex and not daily.

Plan B One-Step is not the same as an abortion pill and does not affect pregnancy in someone already pregnant.

Moreover, it does not protect against sexually transmitted infections (STIs), such as human immunodeficiency virus (HIV).

Overall, Plan B One-Step is only used to prevent pregnancy.

How Effective Is Plan B One-Step?

Plan B One-Step is estimated to be 75% to 89% effective within three days of unprotected sex. The sooner it is taken, the more effective it is.

While Plan B One-Step is commonly called the morning-after pill, you do not have to wait until the morning after having unprotected sex to take this medicine.

Experts recommend keeping a box of Plan B One-Step on hand in your medicine cabinet. This ensures you will have it when needed and can take it immediately.

It is also considered effective, but not as effective, when taken up to five days after unprotected sex. The longer you wait, however, the less effective it is. Also, note that you can still become pregnant later in the same menstrual cycle.

Immediately after taking EC like Plan B One-Step, you should use a barrier contraceptive, such as a condom and your regular birth control method, for at least seven days if you have intercourse.

How Does Plan B One-Step Work?

Plan B One-Step works by stopping or delaying the release of an egg from the ovary (ovulation), therefore creating an undesirable environment for pregnancy.

This action stops the pregnancy from occurring. However, it does not work if ovulation is already occurring and does not affect or terminate (end) a pregnancy in an already pregnant person.

What Medications Interact With Plan B One-Step?

Certain drugs may interact with Plan B One-Step, making it less effective.

Examples of drugs and supplements that have the potential to interact with Plan B One-Step include:

  • Dilantin (phenytoin)
  • Phenobarbital
  • Rifadin (rifampin)
  • Topamax (topiramate)
  • Saint-John's-wort
  • Paxlovid (nirmatrelvir/ritonavir)
  • Sustiva (efavirenz)
  • Tegretol (carbamazepine)
  • Trileptal (oxcarbazepine)

Also, you should not take Plan B One-Step (or any levonorgestrel-based EC) if you have taken the EC drug Ella (ulipristal) in the past five days.

Can Plan B One-Step Cause Side Effects?

Side effects are possible as a result of using Plan B One-Step.

Some common side effects associated with Plan B One-Step include:

  • Menstrual irregularities (your period may come earlier or later than expected, or you may have spotting or a heavier or lighter period than usual)
  • Nausea, vomiting, and diarrhea
  • Stomach pain
  • Fatigue
  • Headache
  • Dizziness
  • Breast tenderness

If you vomit within two hours after taking Plan B One-Step, contact your healthcare provider to determine if you should repeat the dose.

Who Can Take Plan B One-Step?

You can take Plan B One-Step as soon as possible after unprotected intercourse or birth control failure. This can occur when birth control is not used or is used incorrectly, or fails, such as when a condom breaks. Plan B One-Step can also be taken after a sexual assault or rape.

Additional examples of situations where unintended pregnancy may occur could include the following:

Anyone of any age or gender can purchase Plan B One-Step OTC as a prescription, or identification is not required.

You can find Plan B One-Step, or other levonorgestrel-based EC drugs, such as Take Action, My Way, Option 2, My Choice, or Aftera, at several places, including:

  • Pharmacies (it may be kept behind the counter, but still does not require a prescription)
  • Online stores
  • Family planning clinics
  • Health department clinics
  • Planned Parenthood centers

Who Should Not Take Plan B One-Step?

Plan B One-Step is not for everyone.

The following individuals should not take Plan B One-Step:

  • People who are allergic to levonorgestrel or any ingredient in Plan B One-Step
  • People who are pregnant
  • People who have undiagnosed vaginal bleeding

Is Weight a Factor in Who Can Take Plan B One-Step?

Levonorgestrel EC, like Plan B One-Step, may be less effective in females who are overweight or experiencing obesity.

Clinical guidelines state that body weight does not affect another form of EC, the copper intrauterine device (IUD).

Guidelines also state that Plan B One-Step or other forms of oral EC should not be withheld from females who may be overweight or have obesity because research has not established weight guidelines.

However, suppose you are in a situation where you need contraception immediately. In that case, Plan B One-Step or another form of oral EC should be used as soon as possible.

How Much Does Plan B One-Step Cost?

You can purchase Plan B One-Step OTC for about $40 to $50. There are generic products available that may cost between $11 and $45. You can also check with your Planned Parenthood center, family planning clinic, or town health department to see if you can get Plan B One-Step for a lower cost or for free.

Many Medicaid and insurance plans cover Plan B One-Step with no co-pay. Although it's an OTC drug, you will need a prescription from your healthcare provider to apply your insurance to the cost.

You can always purchase Plan B One-Step without a prescription, but insurance would not apply without a prescription.

Is Plan B One-Step Available Generically?

Yes, there are multiple generics available for Plan B One-Step.

All are available OTC; anyone can purchase them, regardless of age or gender, without a prescription or identification.

Some generic alternatives to Plan B One-Step include:

  • Take Action
  • My Way
  • Option 2
  • Preventeza
  • My Choice
  • Aftera
  • AfterPill
  • EContra

Your pharmacy or clinic may carry Plan B One-Step and/or one of the generics. All levonorgestrel-based generics work the same and are as effective as Plan B One-Step.


Plan B One-Step, which contains the ingredient levonorgestrel, is a type of EC that can prevent pregnancy in the event of unprotected sex or birth control failure.

Plan B One-Step is not an abortion pill and does not protect against sexually transmitted infections.

Although Plan B One-Step can work up to several days after the unprotected sex or birth control failure event, it is most effective the sooner you take it.

Because of this, it is best to have it in your medicine cabinet so that if you need it, you can take it immediately.

Anyone of any gender or age can purchase Plan B One-Step OTC without a prescription or identification.

If you have any questions about Plan B One-Step, emergency, or regular contraception, consult your healthcare provider for medical advice.

Frequently Asked Questions

  • Is there a connection between Plan B One-Step and RU-486?

    These two medications are different. Plan B One-Step, often called the morning-after pill, reduces the chance of unintended pregnancy. The abortion pill (RU-486, or mifepristone) ends a pregnancy.

  • How many times can I take EC, like Plan B One-Step, throughout my life?

    You can take EC as often as needed. However, it is not a regular form of birth control or a substitute for birth control. It is only intended to lower the risk of pregnancy after unprotected sex or a birth control failure event.

    If you have unprotected sex a week after taking Plan B One-Step, you must take another dose.

    Plan B One-Step does not protect against future unprotected sex or birth control failure events. Talk to your healthcare provider about the type of regular birth control that would be best for you.

  • If I take EC, will that affect my chance to become pregnant in the future?

    No. Taking Plan B One-Step or another type of EC will not affect your fertility in the future.

  • Do I need to take a pregnancy test after taking EC?

    If you do not get your period within three or four weeks of taking EC, you should take a pregnancy test and consult your healthcare provider.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. DailyMed. Plan B One-Step - levonorgestrel tablet.

  3. Food and Drug Administration. Plan B One-Step (1.5 mg levonorgestrel) information.

  4. American College of Obstetricians and Gynecologists. Emergency contraception.

  5. Prescribers' Digital Reference. Levonorgestrel - drug summary.

  6. MedlinePlus. Emergency contraception.

  7. Kapp N, Abitbol JL, Mathé H, et al. Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraceptionContraception. 2015;91(2):97-104. doi:10.1016/j.contraception.2014.11.001

  8. American College of Obstetricians and Gynecologists. Emergency contraception practice bulletin.

  9. Planned Parenthood. The difference between the morning-after pill and the abortion pill.

  10. World Health Organization. Emergency contraception.

  11. University of Michigan University Health Service. What is emergency contraception?

By Karen Berger, PharmD
Karen Berger, PharmD, is a community pharmacist and medical writer/reviewer.