"It prevents a fertilized egg from attaching…and causes a miscarriage of the baby": A qualitative assessment of how people understand the mechanism of action of emergency contraceptive pills

Contraception. 2021 Jun;103(6):408-413. doi: 10.1016/j.contraception.2021.01.009. Epub 2021 Jan 27.


Objective: The mechanism of action (MOA) of emergency contraceptive pills (ECPs) is frequently mischaracterized. Our objective was to identify how members of the general public understand the mechanisms of ECPs.

Study design: We recruited a convenience sample from social media for a survey about reproductive health attitudes and analyzed spontaneous descriptions of how ECPs work. We inductively coded responses to create themes and subthemes, and collapsed subthemes into three MOA categories based on previous research.

Results: Among 1443 respondents, 533 mentioned an MOA in their description of ECPs. While nearly half of these responses (49.5%) stated that ECPs prevent pregnancy before fertilization occurs (in accordance with most biomedical ECP research), over 60% described a mechanism related to preventing implantation of a fertilized egg. Nine percent of responses described a postimplantation mechanism that would be considered abortion by mainstream medical standards. Some respondents conveyed significant confusion about the biological processes involved with pregnancy and pregnancy prevention.

Conclusion: Confusion about how ECPs work was common among our sample. The largest group of responses described a mechanism-preventing implantation of a fertilized egg-listed on the Food and Drug Administration (FDA)-approved ECP labels that does not reflect most relevant biomedical research. Mischaracterizations of ECPs' mechanisms have been used to limit access to EC. These misunderstandings were common in our sample and may reflect poor quality sex education and public information, and confusion introduced by the FDA-approved labels. Additional research should identify whether public perception of ECPs' mechanisms influences policy, health care provision, and use of ECPs.

Keywords: Emergency contraception; Levonorgestrel; Mechanism of action; Sexual and reproductive health information; Ulipristal acetate.

MeSH terms

  • Abortion, Induced*
  • Abortion, Spontaneous*
  • Contraceptives, Postcoital*
  • Female
  • Humans
  • Pregnancy
  • Reproduction
  • Zygote


  • Contraceptives, Postcoital