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Birth Control Health Center

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Plan B One-Step

Plan B One-Step is a type of emergency contraception. This is birth control that can prevent pregnancy after unprotected sex. People sometimes call it the "morning after pill." But you don't have to wait until the morning after sex to take it. In fact, Plan B is more effective the sooner you take it. It 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.

How Does Plan B One-Step Work?

Depending upon where you are in your cycle, Plan B One-Step may work in one of these ways:

  • It may prevent or delay ovulation.
  • It may interfere with fertilization of an egg.

It is also possible that this type of emergency birth control prevents implantation of a fertilized egg in the uterus by altering its lining.

Plan B One-Step is not the same as RU-486, which is an abortion pill. It does not cause a miscarriage or abortion. In other words, it does not stop development of a fetus once the fertilized egg implants in the uterus. So it will not work if you are already pregnant when you take it.

How Effective Is Plan B One-Step?

If you take it within 72 hours after you've had unprotected sex, Plan B One-Step can reduce the risk of pregnancy by up to 89%. If you take Plan B One-Step within 24 hours, it is about 95% effective.

But you should know that Plan B One-Step is not as effective as regular contraception. So don't take it as your main form of birth control. And, it does not protect you against sexually transmitted diseases. Think of it as a backup -- not for routine use. That's why it's called Plan B.

      Also, research shows that Plan B One-Step starts to lose its effectiveness in women heavier than 165 pounds and is not recommend for anyone over this weight. Instead, a copper-releasing IUD is the suggested option for emergency contraception in this group.

How to Take Plan B One-Step

Plan B One-Step can be purchased over the counter at drugstores without a prescription or proof of age. Because it is most effective when taken as soon as possible (up to 72 hours after sex), consider having a ready supply in your medicine cabinet.

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