Even with protection, there’s a chance of pregnancy. If you’ve turned to Plan B to prevent an unplanned pregnancy, understanding its effectiveness and what happens if it fails is essential. This guide covers how Plan B works, its risks and side effects, and your next steps if pregnancy occurs.
How Does Plan B Work?
Plan B is a form of emergency contraception that lowers the risk of pregnancy by preventing or delaying ovulation. It’s often used when birth control fails or in cases of sexual assault.
However, Plan B doesn’t always prevent ovulation,[1][2][3] but may also work by disrupting the hormonal environment and interfering with the embryo’s attachment to the uterus, resulting in its death.[4]
It’s important to know that Plan B and all other forms of emergency contraception should only be used as backups, not as primary methods of birth control.[5]
Is Plan B the Same as the Abortion Pill?
While they seem similar, Plan B and the abortion pill are not the same things.
The difference is that Plan B aims to keep you from getting pregnant in the first place and may disrupt a newly formed embryo from continuing to grow[6], but the abortion pill is designed to end a pregnancy every single time it is used.
If you’ve been sexually active in the weeks before taking Plan B, consider a pregnancy test or ultrasound to confirm you’re not already pregnant.
Can Plan B Cause a Miscarriage?
A miscarriage is the unintended loss of a pregnancy before 20 weeks. If an embryo has formed when Plan B is taken, it may interfere with uterine attachment, potentially causing the embryo’s termination.[7]
If that is not your intent, then Plan B may not be for you.
How Effective Is Plan B? When Should I Take It?
Plan B is most effective when taken as soon as possible after unprotected sex, ideally within 72 hours. While it significantly reduces the risk of pregnancy, it is not 100% effective.[8]
What Are the Side Effects of Plan B?
Common side effects of Plan B include[9]:
- Dizziness
- Headache
- Abdominal pain or cramps
- Nausea or vomiting
- Breast tenderness
- Delayed period, irregular bleeding, or heavier menstrual bleeding[10]
These side effects are typically mild and resolve within a few days. However, if you experience prolonged bleeding, spotting beyond a week, or severe abdominal pain, contact your healthcare provider immediately. These symptoms could indicate a miscarriage or ectopic pregnancy.[11]
What to Do If Plan B Fails
If you’ve taken Plan B and missed your period, it could mean that you’re pregnant.[12] Take a pregnancy test to confirm. If the result is positive, our compassionate team at [center_name] is here to guide you through your pregnancy options, empowering you to make an informed decision. We offer confidential, free services to support your next steps.
Give us a call at [phone_number_c] or make an appointment online today. All services are confidential and free of charge!
Make an appointment online today.
Please be aware that [center_name] does not provide or refer for abortion services.
Sources
- Hapangama D, Glasier AF, Baird DT. “The effects of peri-ovulatory administration of levonorgestrel on the menstrual cycle.” Contraception. 2001 Mar;63(3):123-9. DOI:10.1016/s0010-7824(01)00186-x https://www.contraceptionjournal.org/article/S0010-7824(01)00186-X/fulltext
- Croxatto, HB, Brache V, Pavez M, Cochon L, Forcelledo ML, Alverez F, Massai R, Faundes A, and Salvatierra AM, 2004. “Pituitary-ovarian Function Following a Standard Levonorgestrel in Emergency Contraception Dose or a Single 0.75 mg Dose Given on the Days Preceding Ovulation.” Contraception. 2004 Dec;70(6):442-50. DOI:10.1016/j.contraception.2004.05.007 https://www.contraceptionjournal.org/article/S0010-7824(04)00156-8/fulltext
- AAPLOG Committee Opinion #7. (2020, January). Embryocidal Potential of Modern Contraceptives. https://aaplog.org/wp-content/uploads/2024/05/Committee-Opinion-7-updated.pdf
- See #3.
- Levonorgestrel (Oral Route) Side Effects. Mayo Clinic. (2024, September 1). https://www.mayoclinic.org/drugs-supplements/levonorgestrel-oral-route/side-effects/drg-20074413
- Kahlenborn, C., Peck, R., & Severs, W. B. (2015). Mechanism of action of Levonorgestrel emergency contraception. The Linacre Quarterly, 82(1), 18-33. https://doi.org/10.1179/2050854914y.0000000026
- See source #6.
- See source #5.
- Mayo Foundation for Medical Education and Research. (2022, June 3). Morning-after pill. Mayo Clinic. https://www.mayoclinic.org/tests-procedures/morning-after-pill/about/pac-20394730#
- See sources #5 and #9.
- See sources #5 and #9.
- See sources #5 and #9.
