What is medication abortion and its drug regimen?

Medication abortion is a two-drug regimen that uses the drugs mifepristone1 (aka Mifeprex and RU-486) and misoprostol.2 The regimen begins with mifepristone ingestion, followed 24–48 h later with 800 mcg of misoprostol taken buccally (in the cheek pouch).3 The FDA manages the regimen under the Risk Evaluation and Mitigation Strategy (REMS). In 2023, the FDA permanently removed the REMS in-person dispensing requirement and added a process to certify pharmacies but retained other REMS requirements, such as the need for prescriber certification.4

Mifepristone (aka Mifeprex, RU486) competes with the mother’s progesterone, a naturally occurring hormone that prepares her body for pregnancy. Progesterone plays a critical role in the normal functioning of the human female reproductive system. It promotes placental development, prepares the uterus for embryo implantation,5 and inhibits uterine contractions.6 Mifepristone is a progesterone receptor antagonist that binds more aggressively to the progesterone receptors in the uterus than progesterone but does not activate the receptor. The primary effect of mifepristone in medication abortion is to cause a separation of the decidua basalis from the trophoblast, which results in the death of the embryo.7 Misoprostol (aka Cytotec) is a prostaglandin E1 analogue that causes cervical softening and uterine contractions, expelling the embryo.8  For additional information refer to Medication Abortion Up to 70 Days of Gestation, Questions and Answers on Mifepristone for Medical Termination of Pregnancy Through Ten Weeks Gestation, and Cytotec misoprostol tablets.9

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  1. FDA. 2016. “MIFEPREX (mifepristone) Medication Guide.” https://www.accessdata.fda.gov/drugsatfda_docs/label/2016/020687s020lbl.pdf. ↩︎
  2. FDA. 2017. “Cytotec misoprostol tablets.” https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/019268s051lbl.pdf. ↩︎
  3. ACOG. 2020. “Medication Abortion up to 70 Days of Gestation.” https://www.acog.org/en/clinical/clinical-guidance/practice-bulletin/articles/2020/10/medication-abortion-up-to-70-days-of-gestation. ↩︎
  4. FDA. 2023. “Mifeprex (Mifepristone) Information.” https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/information-about-mifepristone-medical-termination-pregnancy-through-ten-weeks-gestation ↩︎
  5. Coomarasamy, A., H. Williams, E. Truchanowicz, P. T. Seed, R. Small, S. Quenby, P. Gupta, et al. 2015. “A Randomized Trial of Progesterone in Women with Recurrent Miscarriages.” New England Journal of Medicine 373 (22): 2141‐2148. https://doi. org/10.1056/NEJMoa1504927 ↩︎
  6. Scarpin, Katherine M., J. Dinny Graham, Patricia A. Mote, and Christine L. Clarke. 2009. “Progesterone Action in Human Tissues: Regulation by Progesterone Receptor (Pr) Isoform Expression, Nuclear Positioning and Coregulator Expression.” Nuclear Receptor Signaling 7 (December): e009. https://doi.org/10.1621/nrs.07009. ↩︎
  7. AAPLOG. 2022. “The Reversal of the Effects of Mifepristone by Progesterone, Practice Guideline 6.” https://aaplog.org/wp-content/uploads/2023/01/ PG-6-Reversal-of-the-Effects-of-Mifepristone- by-Progesterone.pdf.  ↩︎
  8. ACOG. 2020. Medication Abortion Up to 70 Days of Gestation. https://www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2020/10/medication-abortion-up-to-70-days-of-gestation. ↩︎
  9. The source of the written content on this page is from Mifepristone Antagonization with Progesterone to Avert Medication Abortion: A Scoping Review under the Creative Commons 4.0 license. No changes were made. ↩︎