How to Use the Plan B Morning-After Pill

Dosage and Safety of Levonorgestrel Emergency Contraceptives

Table of Contents
View All
Table of Contents

Plan B One-Step is the brand name of an oral hormone pill approved by the U.S. Food and Drug Administration (FDA) in 2009 as an effective form of emergency contraception. Also known as the "morning-after pill," Plan B One-Step is used to prevent pregnancy after unprotected sex.

Plan B pills on a surface
Scott Olson / Getty Images

Plan B One-Step consists of one pill containing 1.5 milligrams (mg) of the progestin hormone levonorgestrel. It replaces the original Plan B (sold under the generic name Next Choice), in which two pills are taken.

If used as directed, Plan B One-Step and Next Choice can reduce the risk of pregnancy by around 97%, according to a 2010 study in the Lancet.

Levonorgestrel-only emergency contraceptives can be found on drugstore shelves under such brand names as Take Action, My Way, My Choice, Afterpill, and others.

How They Work

Plan B One-Step and Next Choice work in the same way as progestin-only birth control pills. They cause the mucus in the cervix to thicken, making it difficult for sperm to enter the uterus and fertilize an egg. Levonorgestrel also thins the lining of the uterus, making it near impossible for an egg to implant even if fertilization were to occur.

While effective in preventing birth, a 2015 review in Clinical Obstetrics and Gynecology concluded that the levonorgestrel tablets fell a bit short compared to two other emergency contraceptive options approved by the FDA:

  • Copper intrauterine devices (IUDs) are considered the most effective method overall with a failure rate of only 0.1%. 
  • Ella (ulipristal acetate) is a progesterone agonist that, in real-world testing, was 65% more effective than levonorgestrel in the first 24 hours after sex and 42% more effective in the first 72 hours after sex.

Of the currently approved options, combination progestin/estrogen pills were the least effective overall, nearly doubling the risk of pregnancy versus levonorgestrel alone.

If taken within 72 hours of unprotected sex, levonorgestrel can reduce your risk of pregnancy by around 89%. If taken within 24 hours, it is around 97% effective.

How to Take Them

Although the package insert indicates that Plan B and Next Step are effective for 72 hours after unprotected sex, a number of studies have suggested that they may work for up to five days, albeit with declining efficacy. Clearly, the earlier you start treatment the better.

In the United States, progestin-only emergency contraception is available without a prescription for women 17 and over. You may need to bring some form of ID to prove your age.

If you are under 17, you would need to get a prescription. Most Planned Parenthood centers, women's health clinics, and hospital emergency rooms can provide both a prescription and the emergency contraceptive at the same time.

Plan B One-Step usually costs around $50, while the generics cost about $40 or less. If you would like your health insurance to pay for it, ask your pharmacist for help in submitting a claim.

The dosing instructions for Plan B and Next Step are pretty straightforward;

  • For Plan B One-Step, take one 1.5-mg pill as soon as you can with or without food.
  • For Next Step, you can either take both 0.75-mg pills at the same time or in a divided dose (taking the first pill as soon as you can, followed by the second pill 12 hours later). 

Side Effects

Levonorgestrel is known to cause nausea in some women. To avoid vomiting the pill, take a dose of Kaopectate or Pepto-Bismol (both of which contain (bismuth subsalicylate) if you feel queasy or nauseous. You can also take an over-the-counter antinauseal like Bonine (meclizine), Dramamine (dimenhydrinate), or Valoid (cyclizine).

Other possible side effects include:

  • Headaches
  • Dizziness
  • Breast tenderness
  • Abdominal pain
  • Spotting
  • Changes in your flow (either heavier or lighter)
  • A delayed or early period during your next menstrual cycle

Plan B or Next Step are not known to cause serious complications.


There are some drugs that can interact with Plan B and Next Step by reducing the concentration of levonorgestrel in the blood. While most of these interactions won't undermine the efficacy of emergency contraception, the HIV drug Sustiva (efavirenz) can reduce levonorgestrel concentration by as much as 50%, according to a 2017 study in the journal AIDS.

If taking Sustiva or the combination HIV drug Atripla (which contains efavirenz), speak with your healthcare provider if emergency contraception is needed. A larger dose of Plan B or Next Step may be needed.

Never increase the dose of Plan B or Next Step unless your practitoner tells you to do so. Doing so can increase the risk of side effects, including heavy bleeding and vomiting.

Call your healthcare provider if you have pregnancy symptoms, receive a positive home pregnancy test result, or do not have a period for more than three weeks after taking an emergency contraceptive.

A Word From Verywell

Plan B One-Step or Next Step should not be used as your main form of birth control. The frequent use of progestin-based emergency contraception can cause your periods to become irregular and unpredictable. There are more cost-effective ways to prevent pregnancy than emergency contraceptives.

If unsure about your birth control options, speak with your healthcare provider or visit your nearest Planned Parenthood or women's health clinic.

4 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.
  1. Glasier AF, Cameron ST, Fine PM, et al. Ulipristal acetate versus levonorgestrel for emergency contraception: a randomised non-inferiority trial and meta-analysisThe Lancet. 2010;375(9714):555-562. doi:10.1016/s0140-6736(10)60101-8.

  2. Cleland K, Raymond EG, Westley E, Trussell J. Emergency contraception review: evidence-based recommendations for clinicians. Clin Obstet Gynecol. 2014;57(4):741-50. doi:10.1097/GRF.0000000000000056

  3. U.S. National Library of Medicine. ToxNet Levonorgestrel.

  4. Nanda K, Stuart GS, Robinson J, Gray AL, Tepper NK, Gaffield ME. Drug interactions between hormonal contraceptives and antiretrovirals. AIDS. 2017;31(7):917-952. doi:10.1097/QAD.0000000000001392

By Dawn Stacey, PhD, LMHC
Dawn Stacey, PhD, LMHC, is a published author, college professor, and mental health consultant with over 15 years of counseling experience.