More than 100 scientific studies, spanning continents and decades, have examined the effectiveness and safety of mifepristone and misoprostol, the abortion pills that are commonly used in the United States. All conclude that the pills are a safe method for terminating a pregnancy.
Small icons of scientific papers are lined up in a grid, each representing a study of medication abortion.
A vast majority of the studies report that more than 99 percent of patients who took the pills had no serious complications. These uncommon complications can include hospitalization, blood transfusions or major surgeries.
Safety of abortion pills
Share of patients in each study who did not experience serious complications
A histogram showing that a majority of studies in the Times review found that most patients had no serious complications.
In 86 of 101 studies, almost no patients
had serious complications.
In 86 of 101 studies, almost no patients
had serious complications.
Abortion providers often say that the pills are safer than many common drugs, such as Tylenol and Viagra. Drug safety experts do not typically compare drugs in this way, and they instead assess the safety of a given medication against other choices.
For pregnant women considering medication abortion, the alternatives would be childbirth or procedural abortion.
Serious complication rates
0.16% of patients
“There may be a political fight here, but there’s not a lot of scientific ambiguity about the safety and effectiveness of this product,” said Dr. Caleb Alexander, a professor of epidemiology and medicine at the Johns Hopkins Bloomberg School of Public Health, and a co-director of the Center for Drug Safety and Effectiveness.
Despite the extensive scientific record on the safety of the two abortion pills, anti-abortion groups in the United States have asked a federal judge to issue an order to block the drugs from being used to terminate pregnancies, arguing that they are dangerous.
If upheld by higher courts, a ruling in the plaintiffs’ favor could upend abortion across the country, where more than half of abortions are done with medication. The drugs are typically used through the first 12 weeks of pregnancy.
“The use of these two chemical abortion drugs causes significant injuries and harms to pregnant women and girls,” the anti-abortion groups state in their complaint.
As evidence of this harm, the plaintiffs cite a handful of studies, none of which contradict the body of research in the Times review. Instead, the cited studies point to patient experiences that are common and expected, such as bleeding and pain, or experiences that are not a clear measure of serious complications, such as visits to the emergency room after taking the pills.
Almost all patients will experience bleeding and pain during a medication abortion, because the pills essentially trigger a miscarriage.
Side effects and complications related to abortion pills
Typically resolves without medical intervention.
Fever, warmth or chills
Typically involves medical intervention, at patient’s request or by necessity.
Might cause permanent damage to health without medical intervention.
“It’s not a pleasant experience. The bleeding does naturally make people worry whether it is a normal amount or if the pregnancy tissue has passed,” said Ushma Upadhyay, a professor of reproductive sciences at the University of California, San Francisco.
Some patients who become concerned about the amount of bleeding or other side effects will go to the emergency room after taking the pills, but Dr. Upadhyay’s research shows that most do not face serious complications.
And while the pills are about 95 percent effective, about 3 to 5 percent of patients need an additional procedure to remove remaining tissue or terminate the pregnancy. Providers say these are not typically dangerous situations.
“These are no more risky than if you had a surgical procedure from the beginning,” said Dr. Adam R. Jacobs, the medical director of complex family planning at Mount Sinai Hospital in New York. “Still very safe, with a low risk for complications.”
In the lawsuit against the U.S. Food and Drug Administration that seeks to block the use of the pills, the plaintiffs relied on five studies to argue that the pills cause harm: three from researchers in Finland and two from the Charlotte Lozier Institute, an arm of Susan B. Anthony Pro-Life America.
Research on medication abortion
cited in F.D.A. lawsuit
A diagram compares research papers cited by the F.D.A. with papers cited by the plaintiffs in a lawsuit challenging medication abortion.
Note: Studies that did not measure safety are those that did not report serious complications.
Only one of the studies cited by the plaintiffs reports on serious complications of the abortion pill regimen within the 12-week window typically used in the United States. (Two others looked at safety further along in pregnancy.)
That study reviewed records for more than 40,000 medication abortions conducted in Finland in the early 2000s. It reported that 20 percent of patients followed up with a clinician, most often for bleeding and less commonly for a procedure to evacuate the uterus and complete the abortion.
The plaintiffs and other anti-abortion groups say the 20 percent figure from this single study suggests that patients have a high risk of complications after taking the pills. But the study itself notes that bleeding is expected, serious complications are rare and medication abortion is safe.
A layout of eight scientific studies on medication abortion.
Dr. Oskari Heikinheimo, an author of the Finland study and a professor of obstetrics and gynecology at the University of Helsinki, said in an interview that anti-abortion groups are misinterpreting the data.
“The correct scientific way would be to look at the whole body of evidence,” Dr. Heikinheimo said. “If you just pick the results that you personally like, then that’s pure nonsense.”
In response, Dr. Donna Harrison, the chair of the board of the Alliance for Hippocratic Medicine, the plaintiff in the lawsuit, said that other researchers are calling moderate what she thinks are serious complications.
“I agree with him that you can’t pick and choose the results that you want,” she said. “You have to look at what this means for women.”
One of the most important measures of safety for any medication is the risk of death. Across the 101 studies and 124,000 medication abortions covered in the Times review, researchers reported one death from infection related to the abortion, and one death from unrelated causes.
The U.S. Food and Drug Administration reported that during the period since it approved the regimen in 2000 through June last year, approximately 5.6 million women in the United States took the pills and 28 have died, or 0.0005 percent. The agency reported that some of those deaths may have been because of other causes.
The New York Times reviewed 147 published research articles that examined the safety and effectiveness of mifepristone and misoprostol during the first trimester of pregnancy. The papers were cited in five systematic reviews of medication abortion, and were published from 1991 to 2023. The Times also included research studies used by the F.D.A. in its medical reviews of the drugs, and those cited by the plaintiffs and defendants in Alliance for Hippocratic Medicine v. U.S. Food and Drug Administration.
Many studies reported the number of patients experiencing “serious adverse events,” which generally included blood transfusions, hospitalization, major surgery or serious infection. Emergency department or clinical visits without one of these treatments, or routine but uncommon follow-up procedures to complete an abortion, were typically reported as adverse events, but not serious ones. The Times used these counts of serious adverse events to determine the percentage of patients in each study who did not experience serious complications.
The Times excluded 46 of the studies from the analysis, either because they reported common side effects but did not clearly state whether any serious adverse events had occurred, or because their reported data did not allow for an accurate count. None of the excluded studies concluded that the pills are unsafe.
For studies that reported detailed outcomes without noting which events were serious, The Times counted any reported blood transfusions, hospitalizations, major surgeries, serious infections or deaths as serious adverse events. The Times also discounted any serious complications like heart disease or dengue fever that were reported as unrelated to the medication abortion. Duplicate counts of patients facing more than one serious complication were removed whenever possible, however, double-counting may have slightly reduced the calculated safety rate for some studies.
The Times asked several researchers for feedback on this analysis, including drug safety experts and authors of systematic reviews of abortion safety. These include:
- Dr. Caleb Alexander, professor of epidemiology and medicine at the Johns Hopkins Bloomberg School of Public Health and co-director of the Center for Drug Safety and Effectiveness;
- Dr. Melissa J. Chen, associate professor of obstetrics and gynecology at the University of California, Davis;
- Dr. Oskari Heikinheimo, professor of obstetrics and gynecology at the University of Helsinki;
- Leah Koenig, data analyst, Advancing New Standards in Reproductive Health at the University of California, San Francisco;
- Dr. Nathalie Kapp, chief medical officer, International Planned Parenthood Federation;
- Sarah Raifman, project director, Advancing New Standards in Reproductive Health at the University of California, San Francisco;
- Dr. Maria I. Rodriguez, professor of obstetrics and gynecology at Oregon Health & Science University;
- Ushma Upadhyay, professor with Advancing New Standards in Reproductive Health at the University of California, San Francisco.