Nearly two years after a momentous ruling from the U.S. Supreme Court that led to half of all states banning or restricting abortion access, the top court will hear arguments on Tuesday in a case that could have significant consequences for the availability of the abortion medication mifepristone.

Mifepristone, along with misoprostol, is one of two pills used in the most common type of abortion in the nation.

The arguments, and the resulting opinion, will be watched closely after a 2022 decision in Dobbs v. Jackson Women's Health Organization, which enabled 14 states to completely ban medical abortions.

The development made the U.S. an outlier among Western and advanced nations. For countries that have changed abortion laws so far this century, about 90 per cent made amendments that improved access rather than restricting it further, according to a 2019 Council of Foreign Relations report.

A ruling for the plaintiffs could restrict recent Food and Drug Administration (FDA) changes that have loosened requirements on receiving one of two pills used in this type of abortion. It could also potentially undercut federal regulatory authority over drug safety beyond just this medication.

There were approximately 642,700 medication abortions in the U.S. in 2023, according to a report last week from Guttmacher Institute, an abortion rights advocacy group. That represented about 63 per cent of all estimated abortions, and was up from 53 per cent in 2020 and 39 per cent in 2017.

Mifepristone results in a completed abortion 97.4 per cent of the time, according to the latest FDA data. In 2.6 per cent of cases, a surgical intervention is needed, while in 0.7 of cases, the pregnancy continues.

WATCH | Mifepristone has been in use in U.S. for 23 years:

Media Video | The National : U.S. Supreme Court hears arguments over abortion drug availability

Caption: U.S. Supreme Court justices heard arguments in a case that could limit access to the commonly used abortion drug mifepristone. Since the pandemic, more doctors have dispensed the drug through telemedicine but anti-abortion activists want that stopped.

Open Full Embed in New Tab Loading external pages may require significantly more data usage.

The reduced incidence of surgical abortions has likely been enabled by a couple of FDA changes. In 2016, mifepristone was permitted for use from 10 weeks of gestation, up from previous guidance of seven weeks. In 2021, the FDA relaxed in-person requirements, allowing the pills to be sent through the mail, including by health-care providers who are not physicians.

Taking pills at home to end a pregnancy is less invasive than surgery, more convenient than having to travel to an abortion clinic and more private, allowing women to avoid anti-abortion protesters who picket clinics.

Last year, 85,000 women worked with order-by-mail abortion provider Aid Access to obtain the medication, Dr. Rebecca Gomperts, the group's founder, told the Associated Press. Of those, about 50,000 live in states with abortion restrictions, she said.

The Supreme Court ruling could also impact the major players in retail pharmacy services. In some states, drug stores CVS and Walgreens have announced pilot programs that would allow pharmacists to dispense pills without the need for a physician's referral.

The FDA and Danco, the manufacturer of Mifeprex, the brand name of mifepristone, are the defendants.

The plaintiffs in the Supreme Court case are the Alliance for Hippocratic Medicine, a group of medical associations and four doctors who oppose abortion on religious and moral grounds. They are alleging the FDA overlooked serious safety problems when it made mifepristone easier to obtain. But some legal experts say they will have to show a real risk to women has occurred, not just a hypothetical one.

The FDA says the pills are safe. The prescribing information included in the packaging for mifepristone tablets lists the risk rates for complications: 0.03 per cent to 0.5 per cent for transfusions; 0.2 per cent for sepsis; and 0.04 per cent to 0.6 per cent for hospitalization related to medication abortions. The ranges reflect findings across various relevant studies.

Normal side effects may include nausea, vomiting and diarrhea. Bleeding is normal; very heavy bleeding is uncommon and requires medical attention.

The FDA said last year about 5.9 million women have used mifepristone since it was approved more than 20 years ago. The agency has received 32 reports of deaths in women using the medication, including two involving ectopic pregnancies, which grow outside the womb. The deaths can't be definitively attributed to mifepristone, because in many cases the women had other health conditions and were using other medications.

Earlier this year, a medical journal retracted two studies that the plaintiffs had cited as this case proceeded through the courts, which claimed to show the harms of mifepristone. The studies were supported by the Charlotte Lozier Institute, part of an advocacy group that seeks to end access to abortion.

The plaintiffs also cited three studies from Gynuity Health Projects. The New York-based women's health research group told Reuters it believes the plaintiffs distorted some of the study findings in their legal briefs.

Canada did not authorize abortion medication until 15 years after the U.S. did in 2000. Mifegymiso — the name for the two-pill regimen — became available to Canadians in 2017, although for the first two years, there was a mandatory ultrasound requirement.

As of last year, there was only one authorized supplier of the pills, so shortages have occurred more than once due to production and supply chain issues. Those issues aside, of the nearly 97,000 induced abortions tracked in 2022 by the Canadian Institute for Health Information (CIHI), 39.5 per cent were considered medical abortions as opposed to surgical procedures.

A Supreme Court decision should come by late June in this case.

But legal battles are proceeding over other state-implemented restrictions across the U.S. Next month, the justices will hear arguments over whether a federal law on emergency treatment at hospitals must include abortions, even in states that have otherwise banned them.

Health-care providers have said that if mifepristone is no longer available or is too hard to obtain, they would switch to using only misoprostol, which is somewhat less effective in ending pregnancies and can lead to a higher rate of complications than the two-drug regimen.