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How Does Plan B Affect Your Body?

If you’re sexually active, there’s always a chance that you could get pregnant, even if you’re using protection. Maybe you’re thinking about using Plan B to avoid an unexpected pregnancy.

While it seems like a simple fix, Plan B isn’t foolproof either. It’s important to be aware of how Plan B could affect your body and what to do if it fails!

Today, we’re exploring Plan B—including how it works, the potential risks and side effects, and what to do if you still get pregnant after taking it. Keep reading to learn more!

How Does Plan B Work?

Plan B is a form of emergency contraception that aims to lower the risk of pregnancy by delaying ovulation or preventing fertilization[1]. It’s important to know that Plan B (and all other forms of emergency contraception) should not be used in place of regular birth control[1]. It should also be noted that Plan B tends to be less effective for women who weigh 165 pounds or more[2].

Is Plan B the Same as the Abortion Pill? Can Plan B Cause Miscarriage?

While they seem similar, Plan B and the abortion pill are not considered the same things. The difference is that the goal of Plan B is to delay ovulation altogether, while the abortion pill ends a pregnancy that has already started[1].

That being said, Plan B can fail in preventing ovulation and an egg can still be fertilized. In that case, the fertilized egg would be prevented from implanting into the uterus[3]. The embryo will never have the chance to develop into a viable pregnancy and will eventually be miscarried.

What are the Side Effects of Plan B?

It’s important to be aware of the potential side effects of Plan B so you can make the best decision for your health! Common side effects of Plan B include[1]:

  • Allergic reaction to levonorgestrel (a hormone found in Plan B)

  • Irregular periods

  • Dizziness

  • Headaches

  • Fatigue

  • Breast tenderness

  • Cramps or abdominal pain

  • Nausea or vomiting

Does Plan B Cause Irregular Periods?

You can experience an irregular period after taking Plan B, which can be stressful if you’re concerned about an unexpected pregnancy. You may experience a delayed period (up to a week), heavier bleeding during your next period, or bleeding between periods[1].

If you experience bleeding or spotting for more than a week or severe abdominal pain three to five weeks after taking Plan B, call your doctor immediately. These symptoms can indicate that you became pregnant, but a miscarriage or ectopic pregnancy occurred[1].

What Should I Do if Plan B Fails?

If your period is delayed for more than three to four weeks, it may be a sign that Plan B failed[1]. The next step is to determine whether or not you’re pregnant. Don’t want to take this next step alone? Consider scheduling a free pregnancy test and free ultrasound at Care Net!

If your results come back positive, don’t panic. Our compassionate client advocates are here to help you explore all of your pregnancy options so that you can make an informed and empowered decision! We will answer all of your questions and equip you to take your next steps with confidence!

Don’t wait to get the care you deserve! Give us a call at (406) 549-0406 or schedule your appointment online today!


  1. Mayo Foundation for Medical Education and Research. (2022, June 3). Morning-after pill. Mayo Clinic. Retrieved from

  2. Cleland, K., Raymond, E. G., Westley, E., & Trussell, J. (2014, December). Emergency contraception review: Evidence-based recommendations for clinicians. Clinical Obstetrics and Gynecology. Retrieved from

  3. Embryocidal Potential of Modern Contraceptives. AAPLOG. (2020, January 15). Retrieved from



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