The most common abortion method in the US is at risk of disappearing from the market, at least temporarily, after a Texas judge granted an injunction against the US Food and Drug Administration’s decades-old approval for mifepristone, also known as the abortion pill. The preliminary injunction issued Friday by US District Judge Matthew Kacsmaryk, who was appointed by President Donald Trump, could soon end the sale and distribution of mifepristone — used as part of a two-pill regimen to terminate a pregnancy within the first 10 weeks — while a lawsuit seeking a more permanent ban on the drug proceeds. The Biden administration has seven days to appeal to the 5th US Circuit Court of Appeals.

The FDA gave its approval for mifepristone to terminate early pregnancies over 20 years ago. The anti-abortion groups suing the agency argue that it fast-tracked the regulatory process and did so without sufficient scientific evidence. Decades of research has shown the pill to be safe and effective.

Mifepristone is considered the “standard of care” for medication abortion and miscarriage treatment, according to Hayley McMahon, a public health researcher and doctoral student at the Rollins School of Public Health at Emory University. Without mifepristone patients that want medication abortions, as opposed to in-clinic procedures, have other options. But experts warn that without the pill more people will be forced to carry unwanted pregnancies going forward.

Here’s why anti-abortion groups are going after what some consider the most controversial pill in the world.

What is mifepristone and what is it used for?

Mifepristone is a pill approved for abortion in the US. It works by blocking progesterone, a hormone that’s necessary for a pregnancy to continue. Doctors generally prescribe it with misoprostol, a drug used to treat stomach ulcers, that can also induce contractions. When taken together, the two pills have an over 95% efficacy rate in safely ending pregnancies with no further intervention.

France was the first country to approve mifepristone to terminate pregnancies in 1988. Since then more than 70 countries have followed.Over the years, medication abortion has become increasingly popular in the US because it’s a less invasive and more convenient alternative to having a procedure done at a health-care clinic. As of 2020 more than 50% of all abortions were done using pills. That number is likely higher now due to rule changes that have made it easier to get via telemedicine and sent by mail.

Are there side effects?

Yes, the most commonly reported ones are cramping and prolonged heavy bleeding. Some people may also experience nausea, fever and vomiting. About 1 in 100 people who take the drug experience heavy bleeding that requires surgical intervention, according to the FDA.

How can I get mifepristone now?

State laws on the legality of abortion, including medication abortion, vary widely. Around a dozen states have near-total bans on abortion by any method and 15 states put limits on the pill’s distribution, including requiring people to take it at a doctor’s office.

Before the ruling, states with more liberal abortion laws allowed health clinics and accredited health-care practitioners to prescribe mifepristone in person or via telemedicine and have it sent to their patients’ homes via the mail. Major retail pharmacies Rite Aid Corp., Walgreens Boots Alliance Inc. and CVS Health Corp were also making plans to dispense it at locations where state law allowed.

Increasingly, people living in states with restrictive laws are using telehealth services that operate outside the US to get pills prescribed and shipped from overseas. Aid Access, one such service, said it doesn’t plan to stop distribution in light of the recent ruling.

Why is mifepristone at risk of being taken off the market?

Since the end of Roe v. Wade last year, the abortion landscape in the US has radically changed. The ruling opened the door for states to limit or ban abortion. And while many have adopted restrictions, the Biden administration also eased rules on the pill to make it easier for people to get via telemedicine and pharmacies.

The group behind the lawsuit claims that the FDA “chose politics over science” and fast-tracked approval of mifepristone in 2000 without fully examining its safety. The FDA has refuted this characterization, writing in court documents that the agency followed all necessary procedures and extensively reviewed the available evidence.

In addition to claims about the drug’s initial approval, the group has also taken issue with subsequent changes adopted by the FDA, including a 2016 decision that extended the window of use for the medication from the first seven weeks of pregnancy to the first 10 weeks. They say that this change, along with a recent decision to authorize the medication to be distributed by mail, violates “crucial safeguards” intended to protect patients. The FDA has denied these claims.

Major medical groups, including the American College of Obstetricians and Gynecologists, filed a brief to the court saying mifepristone is safe and effective. “This is not an opinion — it is a fact based on hundreds of medical studies and vast amounts of data amassed over the course of two decades,” the filing read.

Are there alternatives?

Misoprostol, the other pill prescribed with mifepristone, has a high success rate when taken on its own and the World Health Organization recommends its use up to 12 weeks in pregnancy.

Multiple clinics told Bloomberg News that they’re planning on switching over to that drug in light of the ruling. While it’s also safe and effective, research has shown it has as slightly lower success rate and its side effects are more acute. “We have a lot of data showing that people have worse pain and worse nausea with that regimen,” said McMahon, the public health researcher.