The facts about Plan B

Plan B One‑Step® is emergency contraception that works by delaying ovulation. Scientific studies have proven it does not impact the implantation of a fertilized egg.

Plan B One‑Step (Plan B) has been available right off the shelf at all major retailers without a prescription or age restriction since 2013 and has been used by millions of women. Its proven safety and efficacy is supported by a large body of clinical studies and scientific literature.

What Plan B is:

A back‑up emergency contraceptive pill to help prevent unintended pregnancy after unprotected intercourse, a contraceptive failure, or sexual assault.

  • Plan B works by temporarily delaying ovulation (the release of an egg from the ovary).
    • Plan B contains 1.5mg of levonorgestrel. This is the same active ingredient used in many regular oral contraceptives for over 30 years – just at a single, higher dose
    • Scientific data show that Plan B works by delaying or preventing ovulation and does not prevent or interfere with implantation of a fertilized egg
    • Plan B will not affect a pregnancy that has already begun and it will not impact a woman’s future fertility

What the scientific studies tell us

The following list of publications contains comprehensive evidence affirming that Plan B One‑Step emergency contraception does not affect implantation and works to safely help prevent pregnancy before it starts. Each entry below includes a summary of research objectives, conclusion, and citation information (links where available) to review the original literature in full.

  • Marions, 2002; Clinical Study

    Research Objectives: Biopsy for endometrial maturation and markers of endometrial receptivity

    Conclusion: MOA of emergency contraception with levonorgestrel is due to inhibition of ovulation

  • Ortiz, 2004; Animal Study

    Research Objectives: Effects of post-coital and pre-ovulatory levonorgestrel on fertility and ovulation in the Cebus monkey

    Conclusion: Findings do not support that levonorgestrel emergency contraception prevents pregnancy by interfering with post-fertilization events

  • Gemzell-Danielsson, 2004; Review Paper

    Research Objectives: Review levonorgestrel effects on female reproductive functions relevant to emergency contraception

    Conclusion: Levonorgestrel emergency contraception works through blockade or delay of ovulation not inhibition of implantation

  • Sakkar, 2005; Review Paper

    Research Objectives: Emergency contraceptive pills

    Conclusion: Levonorgestrel emergency contraception works by inhibition of ovulation rather than prevention of implantation

  • Lalitkumar, 2007; In-vitro Pharmacology / Modeling

    Research Objectives: Levonorgestrel and attachment of embryos to endometrial construct

    Conclusion: Levonorgestrel did not impair attachment of embryos to the in-vitro endometrial construct

  • Meng, 2009; In-vitro Pharmacology, 12 fertile donors

    Research Objectives: Expression of receptivity markers with levonorgestrel in a 3-D endometrial construct

    Conclusion: Levonorgestrel had no effect on the expression of endometrial receptivity markers studied

  • Baird, 2009; Review Paper

    Research Objectives: Review of emergency contraceptive literature

    Conclusion: No data supporting that levonorgestrel can prevent implantation or impair development of the embryo

  • Palomino, 2010; Clinical Study, n=27

    Research Objectives: Levonorgestrel effect on endometrial receptivity biomarkers

    Conclusion: At time of luteinizing hormone (LH) surge, levonorgestrel does not induce changes in progesterone receptors or endometrial receptivity biomarkers

  • Medard, 2010; Review Paper

    Research Objectives: MOA of levonorgestrel emergency contraception

    Conclusion: Levonorgestrel emergency contraception neither alters endometrial receptivity nor impedes implantation

  • Suárez, 2010; Review Paper

    Research Objectives: Evaluate MOA of levonorgestrel emergency contraception

    Conclusion: No morphological or molecular alterations in the endometrium that could interfere with the implantation of the fertilized egg have been demonstrated

  • Noe, 2011; Clinical Study, n=148 (393 cycles)

    Research Objectives: Determination of levonorgestrel emergency contraception efficacy

    Conclusion: Findings are incompatible with inhibition of implantation by levonorgestrel emergency contraception in women

  • Vargas, 2012; Clinical Pharmacology study

    Research Objectives: Endometrial gene expression profile during the receptive period after levonorgestrel emergency contraception dosing

    Conclusion: Observed changes do not endorse hypothesis that levonorgestrel interferes with endometrial receptivity

  • Gemzell-Danielsson, 2014; Review Paper

    Research Objectives: Overview of MOA of oral emergency contraceptive pills

    Conclusion: Levonorgestrel emergency contraception does not impair endometrial receptivity or embryo implantation

  • ESHRE Capri Workshop## Group (Baird et al, 2015); Review Paper

    Research Objectives: Review of emergency contraception, data and global use.

    Conclusion: Peri- and post-ovulatory administration of levonorgestrel emergency contraception does not significantly affect endometrial morphology or corpus luteum function and does not prevent an embryo attaching to the endometrium in vitro. When implantation has already occurred levonorgestrel emergency contraception has no impact on the pregnancy or the newborn

# ISGE: International Society of Gynecological Endocrinology
## ESHRE: European Society of Human Reproduction and Embryology

References

  • Baird DT. Emergency contraception: how does it work? Reprod Biomed Online, 2009; 18 Suppl 1:32-6.
  • ESHRE CapriWorkshop Group, ESHRE Capri Workshop Group, D.T. Baird, S. Cameron, J.L.H. Evers, K. Gemzell-Danielsson, A. Glasier, C. Moreau, J. Trussell, H. von Hertzen, P.G. Crosignani, C. La Vecchia, A. Volpe, A. Glasier, P.G. Crosignani. Emergency contraception. Widely available and effective but disappointing as a public health intervention: a review. Hum Reprod, 2015; 30(4):751–760.
  • Gemzell-Danielsson K, Marions L. Mechanisms of action of mifepristone and levonorgestrel when used for emergency contraception. Hum Reprod Update, 2004; 10:341–348.
  • Gemzell-Danielsson K, Berger C, Lalitkumar PG. Mechanisms of action of oral emergency contraception. Gynecological Endocrinology, 2014; 30:685-7
  • Lalitkumar PG, Lalitkumar S, Meng CX, et al. Mifepristone, but not levonorgestrel, inhibits human blastocyst attachment to an in vitro endometrial three-dimensional cell culture model. Hum Reprod, 2007; 22:3031–7
  • Marions L, Hultenby K, Lindell I, Sun X, Ståbi B, Gemzell Danielsson K. Emergency contraception with mifepristone and levonorgestrel: mechanism of action. Obstet Gynecol, 2002; 100(1):65-71.
  • Medard LM, Ostrowska L. Hormonal (levonorgestrel) emergency contraception--effectiveness and mechanism of action. Ginekol Pol, 2010; 81(7):532-6.
  • Meng CX, Andersson K, Bentin-Ley U, Gemzell-Danielsson K, Lalitkumar, PG. Effect of levonorgestrel and mifepristone on endometrial receptivity markers in a three-dimensional human endometrial cell culture model. Fertil. Steril, 2009; 91, 256–264.
  • Noé G, Croxatto HB, Salvatierra AM, Reyes V, Villarroel C, Muñoz C, Morales G, Retamales A. Contraceptive efficacy of emergency contraception with levonorgestrel given before or after ovulation. Contraception. 2011; 84:486-92.
  • Ortiz ME, Ortiz RE, Fuentes MA, Parraguez VH, Croxatto HB. Postcoital administration of levonorgestrel does not interfere with postfertilization events in the new-world monkey Cebus apella. Hum Reprod. 2004; 19(6):1352-6.
  • Palomino W, Kohen P, Devoto L. A single midcycle dose of levonorgestrel similar to emergency contraceptive does not alter the expression of the L-selectin ligand or molecular markers of endometrial receptivity. Fertil. Steril, 2010; 94, 1589–1594.
  • Sarkar NN. The potential of mifepristone (RU-486) as an emergency contraceptive drug. Acta Obstet Gynecol Scand, 2005; 84(4):309-16.
  • Suárez VJ, Zavala R, Ureta JM, Hijar G, Lucero J, Pachas P. Effect of Levonorgestrel in the Ovoluation, Endometrium, and Spermatozoa for Emergency Oral Contraception.. Rev Peru Med Exp Salud Publica, 2010; 27(2): 222-30
  • Vargas MF, Tapia-Pizarro AA, Henriquez SP, et al. Effect of single post-ovulatory administration of levonorgestrel on gene expression profile during the receptive period of the human endometrium. Journal of Molecular Endocrinology, 2012; 48:25–36.