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Can Plan B make your period late or cause bleeding?

Medically reviewed by Sally Chao, MD. Last updated on July 30, 2021.

Official answer

by Drugs.com

Yes, Plan B (levonorgestrel) can delay your period or cause bleeding to occur outside of regular menstrual bleeding because levonorgestrel is a synthetic hormone. To prevent pregnancy, Plan B, like other birth control pills, must alter your hormone levels, which can prompt these menstrual changes. Plan B is associated with more menstrual changes than regular birth control pills because the dosage is higher.

Changes in the menstrual cycle

In a clinical trial, 31% of participants experienced some change in their menstrual cycle after taking Plan B, but the potential menstrual changes are varied. Plan B may cause some women to experience heavier or lighter menstrual bleeding compared to their regular periods.

After taking Plan B, some women get their period sooner than expected, while others get it later. However, clinical trial data suggest most women will get their period within two days to one week of the anticipated time. Women who take Plan B and experience a delay in their period greater than one week are recommended to take a pregnancy test.

During your menstrual cycle, the time at which Plan B is taken can affect how your menstruation changes.

  • Some studies suggest that taking Plan B early on in your menstrual cycle can increase the likelihood of spotting before menstruation begins and can sometimes cause the next period to be shorter than usual.
  • When Plan B is taken later in your menstrual cycle, it may not affect period length, or it may be more likely to result in prolonged menstrual bleeding.

Spotting

Non-menstrual bleeding, or spotting, can also occur after using Plan B. Clinical trial data show that 16% of participants experienced spotting in the first week after taking Plan B. Similarly, in one study of 232 women who took Plan B, just under 15% experienced spotting. In this study group, the bleeding typically started around 4 days after Plan B was taken and lasted an average of 2.4 days, with a range of one to seven days. Some women began spotting as early as 8 hours after taking Plan B.

Menstrual changes and irregular bleeding associated with Plan B should go away without treatment. In one study of 132 women, most women returned to their normal cycle length in the next cycle following the use of Plan B. However, those who took Plan B later on in their cycle (after ovulation) had a slightly longer next cycle on average.

References
  1. U.S. Food and Drug Administration (FDA). FDA's Decision Regarding Plan B: Questions and Answers. Last reviewed: December 7, 2015. Available at: https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fdas-decision-regarding-plan-b-questions-and-answers. [Accessed July 12, 2021].
  2. The American College of Obstetricians and Gynecologists (ACOG). Practice Bulletin: Emergency Contraception. Last reviewed: September 2015. Available at: https://www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2015/09/emergency-contraception. [Accessed July 12, 2021].
  3. U.S. Food and Drug Administration (FDA). Plan B One-Step (levonorgestrel) tablet, 1.5 mg, for oral use. Last reviewed: July 2009. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2009/021998lbl.pdf. [Accessed July 9, 2021].
  4. Cleland K, Raymond EG, Westley E, Trussell J. (2014) Emergency contraception review: evidence-based recommendations for clinicians.Clin Obstet Gynecol. 57(4):741-750. doi:10.1097/GRF.0000000000000056.
  5. Gainer E, Kenfack B, Mboudou E, Doh AS, Bouyer J. (2006) Menstrual bleeding patterns following levonorgestrel emergency contraception.Contraception. 74(2):118-124. https://doi.org/10.1016/j.contraception.2006.02.009.

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