How Plan B Works

A backup plan you can feel confident about

If you’re going to take Plan B, you want to know how it works. So let’s start with the facts.

What Plan B is:

  • Progestin‑only emergency contraception that works by delaying ovulation

    Similar to birth control pills, Plan B works by delaying or stopping the release of an egg from the ovary.

  • The same active ingredient as regular birth control pills—just at a higher dose

    It’s a single tablet that contains levonorgestrel, 1.5 mg, an ingredient that’s been safely used in many birth control pills for decades.

  • Won’t hurt your chances of getting pregnant later on

    Not ready right now, but think you might want to get pregnant in the future? While it does help prevent pregnancy after unprotected sex, it won’t hurt your ability to get pregnant later on.

What Plan B isn’t:

  • Not an abortion pill

    It won’t affect an existing pregnancy.

  • Not regular birth control

    It’s not meant to be used as a regular birth control method.

  • Won’t protect against HIV/AIDS or other STDs

    Plan B will help prevent pregnancy before it starts, but it won’t prevent any sexually transmitted diseases. You should always use a barrier method, like condoms, to prevent STDs.

Plan B is safe and effective

Plan B contains levonorgestrel—the same active ingredient used in many popular birth control pills—just at a single, higher dose. That said, it shouldn’t be used as regular birth control. If you find that you have had to use emergency contraception multiple times, talk to your doctor about finding a regular birth control method that’s right for you.

Common Plan B side effects

Some women may experience side effects, including:

  • A period that’s lighter, heavier, early, or late
  • Nausea
  • Lower abdominal cramps
  • Tiredness
  • Headache
  • Dizziness
  • Breast tenderness
  • Vomiting

Some women taking Plan B One‑Step® may have changes in their period, such as spotting or bleeding before their next period. If your period is more than a week late, it’s possible you might be pregnant. Get a pregnancy test and follow up with your healthcare professional.

If you vomit within 2 hours of taking Plan B, talk to your healthcare professional to find out if you should repeat the dose.

Still have questions?

We’ve got you covered.

See all FAQs