Is It Safe to Take Plan B While on the Pill?

Medically reviewed by Alan Carter, PharmD on June 22, 2017Written by Kimberly Holland on February 3, 2016

Emergency contraception may be an option if you’ve had unprotected sex or experienced birth control failure. Examples of a contraceptive failure include forgetting to take a birth control pill or having a condom break during sex. Keep these points in mind when deciding if Plan B is the right step for you.

What is Plan B?

Plan B One-Step is the name of an emergency contraceptive. It contains a high dose of the hormone levonorgestrel. This hormone is used at lower doses in many birth control pills, and it’s considered very safe.

Plan B works to prevent pregnancy in three ways:

  • It stops ovulation. If taken before you ovulate, Plan B can delay or stop ovulation if it were going to occur.
  • It prevents fertilization. Plan B alters the movement of the cilia, or the tiny hairs present in the fallopian tubes. These hairs move the sperm and egg through the tubes. Altering the movement makes fertilization very difficult.
  • It prevents implantation. Plan B may affect your uterine lining. A fertilized egg needs a healthy uterine lining to attach to and grow into a baby. Without that, a fertilized egg cannot attach, and you will not become pregnant.

Plan B can help prevent 7 out of 8 pregnancies if you take it within 72 hours (3 days) of having unprotected sex or experiencing a contraceptive failure. Plan B becomes less effective as more time passes after the first 72 hours since these events.

How Plan B interacts with the birth control pill

People taking birth control pills can take Plan B without any complications. If you’re taking Plan B because you skipped or missed more than two doses of your birth control pill, it’s important you resume taking it as scheduled as soon as possible. Use a backup birth control method, such as condoms, for the next seven days after you take Plan B, even if you’ve resumed taking your birth control pills.

Read more: Emergency contraception options »

What are the side effects of Plan B?

Many women tolerate the hormones in Plan B very well. Although some women can take Plan B without experiencing any side effects, others do. Potential side effects can include:

Plan B may delay your period by up to a week. If you don’t get your period within one week after you expect it, take a pregnancy test.

If side effects of the emergency contraception pill don’t seem to resolve within a month, or if you experience bleeding or spotting for several weeks straight, you should make an appointment with your doctor. You may be experiencing symptoms of another issue, such as a miscarriage or an ectopic pregnancy. An ectopic pregnancy is a potentially life-threatening condition that occurs when a fetus begins developing in your fallopian tubes.

Risk factors to keep in mind

Emergency contraception such as Plan B isn’t recommended for overweight or obese women. Research has shown that obese women are three times more likely to become pregnant due to emergency contraception failure.

If you’re overweight or obese, consult your doctor before taking Plan B. They may suggest another option for emergency contraception that could be more effective, such as the copper IUD.

What to expect after using Plan B

Plan B has shown no long-term consequences or issues, and it’s safe for almost every woman to take, even if you’ve been taking another birth control pill. In the days and weeks after taking Plan B, you may experience mild to moderate side effects. For some women, the side effects may be more severe than for others. Some women experience no problems at all.

After the initial wave of side effects, you may experience changes in your period for a cycle or two. If these changes don’t resolve, make an appointment with your doctor to discuss what other issues might be occurring.

Plan B is highly effective if taken properly. However, it is only effective as an emergency contraceptive. It shouldn’t be used as routine birth control. It isn’t as effective as other forms of birth control, including birth control pills, intrauterine devices (IUDs), or even condoms.

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