Abortion pill reversal is a protocol that involves taking high doses of progesterone after swallowing the first medication abortion pill (mifepristone) but before taking the second (misoprostol), with the goal of continuing the pregnancy. The idea is that flooding the body with progesterone can outcompete mifepristone at hormone receptors and keep the pregnancy viable. It remains deeply controversial: proponents claim success rates between 64% and 68%, while the American College of Obstetricians and Gynecologists (ACOG) says the procedure is “unproven and unethical.”
How Medication Abortion Works in Two Steps
Standard medication abortion uses two drugs taken in sequence. The first, mifepristone, blocks the body’s progesterone receptors. Progesterone is the hormone that maintains the uterine lining and supports early pregnancy, so when mifepristone locks onto those receptors, it prevents progesterone from doing its job. The uterine lining begins to break down, and the embryo loses its blood supply.
The second drug, misoprostol, is typically taken 24 to 48 hours later. It causes the uterus to contract and expel the pregnancy. Abortion pill reversal targets the window between these two medications, before misoprostol is taken.
The Theory Behind Reversal
The reversal protocol is based on a straightforward idea: if mifepristone works by blocking progesterone receptors, then giving a large amount of progesterone might overwhelm the blockade through sheer volume. Progesterone receptors function like locks. Mifepristone fits into those locks but doesn’t activate them, effectively jamming the system. Flooding the body with progesterone is intended to push mifepristone off enough receptors that progesterone can resume its normal role of stabilizing the uterine lining and supporting the pregnancy.
There is some biological plausibility to this. Progesterone does have a strong protective effect against pregnancy loss driven by inflammation, which is one mechanism through which mifepristone works. However, research on the cellular level suggests that once mifepristone has triggered cell death in placental tissue, progesterone’s ability to reverse that process is limited. The protection appears to come mainly from suppressing inflammation rather than undoing damage already underway.
What the Protocol Looks Like
There is no single standardized protocol. The progesterone used in reversal attempts has been given by injection, taken orally, or inserted vaginally, with doses ranging from 200 mg to 400 mg on varying schedules. Some published regimens involve daily injections for the first few days, tapering to twice weekly for weeks or months. Others use vaginal progesterone twice daily for several days, then taper to nightly doses.
Proponents recommend starting progesterone within 24 hours of taking mifepristone for the best chance of success. The treatment often continues for weeks or months into the pregnancy. The Abortion Pill Rescue Network, operated by the anti-abortion organization Heartbeat International, connects callers with providers who prescribe the protocol and reports that more than 8,000 births have resulted from its referral system.
What the Evidence Actually Shows
The claimed 64% to 68% success rates come from a 2018 case series led by George Delgado, the physician who pioneered the protocol. ACOG and other medical organizations have pointed to serious problems with this research. The original studies had no control group, meaning there was no comparison to women who took mifepristone alone and did nothing afterward. This is a critical gap, because mifepristone by itself (without misoprostol) does not end every pregnancy. Some pregnancies would continue regardless of any intervention.
The studies also lacked oversight from an institutional review board, the independent committee that protects people enrolled in research. Safety outcomes were not consistently reported, and data collection was incomplete. ACOG describes case series without control groups as “among the weakest forms of medical evidence.”
The one study designed to test the protocol rigorously, with a control group and proper ethics oversight, was stopped early in 2020 due to safety concerns. Three participants experienced severe hemorrhaging, and the researchers concluded it was not safe to continue the trial. That study enrolled too few participants before it was halted to draw reliable conclusions about effectiveness.
Safety Concerns
Taking mifepristone and then not following through with misoprostol creates a situation the body wasn’t designed to handle cleanly. The pregnancy may continue, or it may fail partially. An incomplete process can lead to heavy bleeding, infection, or the need for emergency surgical intervention. The 2020 clinical trial that was stopped early illustrated this risk directly: participants who received no progesterone (the placebo group) experienced hemorrhaging severe enough to require hospital care.
Progesterone itself is generally considered safe during pregnancy and is used in other medical contexts, such as preventing preterm birth in high-risk pregnancies. The concern is not so much about the progesterone as about the unpredictable situation created by taking mifepristone without completing the abortion process, whether or not progesterone is added afterward.
Where Medical Organizations Stand
ACOG’s position is unambiguous: “So-called abortion ‘reversal’ procedures are unproven and unethical.” The organization argues that the existing evidence does not demonstrate that progesterone caused any of the continued pregnancies reported in case studies, since some would have continued on their own. ACOG also objects to state laws that require doctors to tell patients about the reversal option, calling these mandates “dangerous political interference” that compromises patient care.
The American Medical Association has taken a similar stance, opposing legislative requirements to discuss unproven treatments. On the other side, organizations like Heartbeat International and the American Association of Pro-Life Obstetricians and Gynecologists actively promote the protocol and maintain networks of providers willing to prescribe it.
State Laws Requiring Reversal Disclosure
As of late 2021, 14 states had passed laws related to medication abortion reversal. In 12 of those states, patients must be told about the possibility of reversal during pre-abortion counseling. Thirteen states specify that a physician or other healthcare professional must deliver this information. These states include Arkansas, Idaho, Indiana, Kentucky, Louisiana, Montana, Nebraska, North Dakota, Oklahoma, South Dakota, Tennessee, Utah, and West Virginia. Arizona’s law assigns the disclosure to clinic staff rather than a specific type of clinician.
These laws are contentious precisely because they require clinicians to present information that major medical organizations say is not supported by reliable evidence. Some healthcare providers view the mandates as forcing them to share misleading information, while supporters argue patients deserve to know every available option.
The Bottom Line on Effectiveness
Without a completed, well-designed clinical trial, the core question remains unanswered: does progesterone actually increase the chances of a pregnancy continuing after mifepristone, or would many of those pregnancies have survived anyway? Mifepristone alone, without misoprostol, has a known failure rate. Estimates vary, but studies suggest that somewhere between 20% and 50% of pregnancies may continue when only mifepristone is taken, depending on gestational age and other factors. The claimed reversal success rates of 64% to 68% need to be interpreted against that backdrop. Until a properly controlled study is completed, it is impossible to separate the effect of progesterone from the natural failure rate of mifepristone used alone.