In Glenwood Springs, Colorado, registered nurse Katie Laven answers calls from people who've started the two-pill medication abortion regimen and want to stop the process.

"They are just in turmoil," said Laven, who works at the Abortion Pill Rescue Network and answers some of the roughly 150 calls it says come in each month. "They feel like, 'Well, maybe an abortion would make it better.' And then they take the abortion pill and they’re like, 'I don’t feel better. In fact, I feel much worse that I did that.'"

The Abortion Pill Rescue Network is run by Heartbeat International, an anti-abortion group that promotes a controversial practice called abortion pill reversal, in which a patient is given progesterone within 72 hours of taking mifepristone, the first pill administered in a medication abortion, and before taking misoprostol, the second pill. The organization said more than 4,000 infants have been born since 2013 after people went through the reversal process. KFF Health News couldn't independently verify that number, which Heartbeat International said is based on internal patient data.

But such interventions may be coming to an end in Colorado, which recently became the first state to ban abortion pill reversals. The Colorado legislature passed a bill to make prescribing any drug in this way medical misconduct, unless three of the state's medical boards find it is a "generally accepted standard of practice." Democratic Gov. Jared Polis signed the bill into law on April 14.

The bill also limits advertising by pregnancy resource centers, which do not offer abortions; rather, they are known to try to talk people out of getting an abortion.

The Colorado attorney general's office, several district attorneys, the Colorado Medical Board, and the Colorado Board of Nursing said they would not enforce the new law until the two medical boards determine whether abortion reversal is "a generally accepted standard of practice," The Colorado Sun reported.

Pills have emerged as the latest front in the war over abortion since the U.S. Supreme Court overturned Roe v. Wade in June 2022. In early April, a federal judge in Texas ruled to halt access to mifepristone nationwide, a decision later stayed by the Supreme Court.

"The push to promote so-called medication abortion reversal is part of a larger strategy that aims to misinform the public about abortion safety, about the effectiveness of abortion methods, about people who are seeking abortion care and how sure they are of their decision," said Daniel Grossman, director of Advancing New Standards in Reproductive Health (ANSIRH) at the University of California-San Francisco. "All of that misinformation has played an important role in eroding people’s rights to this essential component of health care."

For Laven, the nurse who works for the Abortion Pill Rescue Network hotline, abortion pill reversal is another aspect of patient choice.

"We should not be forcing them to continue," she said of pregnant people. "We should give them the choice to stop if they want."

In 2020, medication abortion accounted for more than half of all documented abortions, according to the Guttmacher Institute, a research organization that supports abortion rights. During the pandemic, the FDA eliminated a long-standing rule that abortion pills be picked up in person, paving the way for patients to receive them in the mail.

There is no comprehensive public data on how often a person takes the first abortion pill then changes their mind. Andrea Trudden, Heartbeat International's vice president of communications and marketing, said in a statement that about 150 women a month start the reversal process through its network, but she did not respond to requests for more details.

"No woman should be forced to complete an abortion she no longer wants," Trudden said. "Imagine knowing that there is a way you can try to save your baby and not be allowed to. It’s not right.”

Abortion rights advocates said patients do sometimes change their minds, even though doctors typically counsel patients beforehand that it's not a reversible process. Doctors can recommend that they induce vomiting if less than an hour has passed since taking mifepristone or else tell them to forgo the second pill, misoprostol. They also cited ANSIRH's Turnaway Study, which tracked more than 600 people who had abortions in the United States for five years afterward, and found that more than 95% felt abortion had been the right decision for them.

Abortion pill reversal is "not based on science," according to the American College of Obstetricians and Gynecologists, which says mandates "based on unproven, unethical research" are dangerous to women's health care. By 2021, 14 states had enacted laws that required patients to receive information on abortion pill reversal, largely during pre-abortion counseling, according to a study in the American Journal of Public Health.

Earlier this month, the Republican-controlled Kansas legislature passed a bill that would require providers to tell patients that medication abortions are reversible once underway. The bill was vetoed by the state's governor then overridden by the legislature. It goes into effect in July.

The practice is also not supported by the American Medical Association, which filed a lawsuit in North Dakota in 2019 challenging two laws that required physicians to tell patients about abortion pill reversal and that abortion terminates "the life of a whole, separate, unique, living human being." That case is pending while a separate lawsuit challenging North Dakota's abortion ban plays out.

Proponents of abortion pill reversal point to a case study led by an anti-abortion physician, George Delgado, president of the Steno Institute, a nonprofit devoted to what the institute calls "pro-life" research. The retrospective analysis reviewed 547 cases and found 64%-68% of patients given progesterone continued their pregnancies after taking mifepristone.

But the study elicited criticism for several reasons, including its methods and lack of safety data. Mifepristone alone is not a very effective abortifacient, according to ANSIRH. In a 1988 study that looked at continued pregnancy in 30 women after they took 200 milligrams of mifepristone, 23% of women continued their pregnancies. The women in that study were no more than seven weeks pregnant.

Delgado’s analysis compared its continued-pregnancy rate, which included women who were anywhere from five to nine weeks pregnant, to that study. Grossman and other authors who reanalyzed the Delgado case series at seven weeks gestation found no significant difference in patients who took progesterone reversal treatment and those who took only mifepristone.

"For now, any use of reversal treatment should be considered experimental and offered only in the context of clinical research supervised by an institutional review board," Grossman and a co-author wrote in a paper in the New England Journal of Medicine.

In 2020, researchers from the University of California-Davis set out to evaluate abortion pill reversal treatment in a controlled trial. That study ended early due to safety concerns. Three women, two in the control group and one in the experimental group who received progesterone, hemorrhaged.

"It’s a very small study, so it’s hard to draw a definitive conclusion, but it certainly is concerning," said Grossman. "And it’s surprising that all of the reports that have come from Delgado, including the largest case series, don’t have any reports of patients having heavy bleeding. And that just really makes me concerned that they weren’t adequately capturing those kinds of safety outcomes."

Delgado, who is a plaintiff in the Texas case against mifepristone, refuted the arguments against his research. He said the case study is one piece of evidence to support abortion pill reversal, alongside other safe uses of progesterone, animal case studies, and the more than 4,000 reversals documented by Heartbeat International.

“Abortion pill reversal has been demonstrated to be safe. It’s been demonstrated to be effective,” he said. “And in my experience in talking to women that I’ve treated, and in talking to other women who have been treated by others, women who are given that opportunity to reverse their chemical abortions have expressed great gratitude. And I’ve never had a woman tell me that she regretted attempting to reverse her chemical abortion.”

Colorado legislators targeted pregnancy resource centers and abortion pill reversal as part of a broader package of abortion rights policy proposals. The other bills in the package protect providers and patients of abortion care and gender-affirming care and expand funding for abortion services, both of which Polis signed into law.

Last year, the Democratic-led legislature passed the Reproductive Health Equity Act, which codified the right to an abortion and contraceptives in state law and declared that an embryo or fetus does not have rights under state law.

As a result of those protections and bans in neighboring states, Colorado has seen an influx of out-of-state patients seeking abortions. In 2022, 3,835 people from out of state received abortions in Colorado, according to provisional data from the state Department of Public Health and Environment. That is 2,275 more people than state officials recorded the year before.

This article was reprinted from khn.org with permission from the Henry J. Kaiser Family Foundation. Kaiser Health News, an editorially independent news service, is a program of the Kaiser Family Foundation, a nonpartisan health care policy research organization unaffiliated with Kaiser Permanente.