WASHINGTON — The future of abortion in the U.S. is moving to the mailbox.

Medication abortion, in which a woman takes two drugs to terminate an early pregnancy at home, became the most commonly used method in the U.S. during the COVID-19 pandemic, particularly after the Food and Drug Administration stopped requiring the prescription be dispensed at healthcare facilities and allowed it to be delivered directly to users. Many online pharmacies around the world ship them without a prescription at all.

As the Supreme Court prepares to give states the power to ban abortion, medication abortion could be a game changer — the last option for women in conservative states who are unable to travel elsewhere to end their pregnancies.

“We see medication abortion as being a potentially transformative and disruptive technology in the face of these unjust laws that are being passed,” said Elisa Wells, co-founder and co-director of Plan C, a website that provides information on finding and using the medication. “It is a bit of a safety net, potentially.”

Medication can be shipped discreetly, in some cases evading detection from those who hope to ban its use. It is so hard to track that statistics on so-called self-managed medication abortions — those conducted without a prescription or a doctor’s guidance — are not well researched.

“It will be very different from the pre-Roe era when abortion was illegal in that it’s harder to restrict pills,” said Dr. Daniel Grossman, an abortion provider and director of Advancing New Standards in Reproductive Health at UC San Francisco. “It’s easier to potentially access them through various channels. And the pills are very safe and effective, unlike ... methods of unsafe abortion or methods that people might have used on their own in the 1960s.”

But just as abortion rights supporters look to shore up access to medication abortion, antiabortion groups are focusing on enacting additional state restrictions on pills, making medication the next battleground in the decades-long cultural standoff over abortion.

“It’s one of our biggest priorities and it’s certainly something that a lot of states are thinking about much more than they were three years ago,” said Katie Glenn, government affairs counsel at Americans United for Life, a law firm that opposes abortion and advises states on legislation. “We saw a huge uptick in the pill use during COVID.”

The process of a medication abortion consists of two drugs taken in succession. Mifepristone is taken first to block the effects of progesterone, a hormone needed to sustain a pregnancy. The second medication, misoprostol, is taken one or two days later to generate cramping and bleeding, like an early miscarriage.

A 2015 study showed that at nine weeks of pregnancy or less, medication abortion was successful 99.6% of the time.

Even so, medication abortion “is not a solution to the problem” of a Supreme Court ruling that undermines abortion rights, Grossman said.

Obstacles may include the drug’s costs, shipping delays, legal risks and the relatively short recommended 10-week window for use. A medication abortion also takes longer than an in-office procedure, and sometimes patients worry they’ve used them incorrectly.

But in states that plan to limit or ban abortion — more than two dozen in the South and portions of the Mountain West have already done so or plan to — medication abortion is likely to be one of the few remaining options.

PlanCPills.org runs through the practical options for residentsof every state, though in some cases, shipping drugs or taking them may violate local laws.

For instance, a patient in Texas — where abortion is banned after embryonic cardiac activity is detected, or about six weeks of pregnancy — could drive across the border into New Mexico and conduct a telehealth appointment with a doctor there. The pills could be shipped to a friend or a temporary mailbox in New Mexico and then forwarded to the patient in Texas. Or a patient could stay in Texas and buy the drugs directly from an online pharmacy at a cost of $200 to $500.

Established as President Trump took office on a vow to appoint only antiabortion justices, Plan C was inspired by the accessibility of abortion pills in other countries, such as Ethiopia, where pharmacies sold them for $7 without a prescription, Wells said. In the U.S. at the time, the medication could cost several hundred dollars and required an in-person visit with a doctor and a prescription.

Once the FDA dropped the in-person requirement at the start of the COVID-19 crisis, medication abortions overtook in-clinic procedures as the most common method of abortion in the United States, according to the Guttmacher Institute, a research group that supports abortion rights.

The impending Supreme Court decision on Roe vs. Wade and states’ moves to curtail abortion access only fueled more interest in the medication. Before the enactment of the Texas six-week abortion ban, Wells’ site got about 500 visitors a day. After enactment, that figure shot up to 25,000 and has since settled at about 2,000, she said.

At Aid Access, perhaps the best-known medication abortion site, U.S. users are put in touch with a European healthcare provider and can get a prescription filled by a pharmacy in India. It costs $110 and delivery takes up to four weeks.

Conservative states are already moving to restrict the ease with which abortion pills can be dispensed.

South Dakota tried requiring four trips to a clinic to get a medication abortion, but the rule was blocked by the courts. A Texas law prohibits medication abortions after seven weeks of pregnancy, even though the FDA says 10.

Nineteen states prohibit pills from being prescribed via telehealth appointments or delivered in the mail, and 32 states limit which healthcare professionals can prescribe abortion pills, according to Guttmacher.

Mailing abortion pills to a patient is banned in Arizona, Arkansas and Texas. Similar bans in Montana, Oklahoma and South Dakota were blocked by the courts.

Just this year, more than a dozen states introduced restrictions on medication abortion, including complete bans, a prohibition on mailing pills and a ban on using telehealth to provide them.

Others are focusing on banning all self-managed abortions. The practice is illegal in Nevada, South Carolina and Oklahoma, but patients have been arrested in other states too.

Most recently, a Texas woman, Lizelle Herrera, was charged with murder because she self-managed an abortion. The charges were later dropped.

Abortion opponents are encouraging states to turn their focus to banning early abortions, when medication is most often used.

“Some states will only go as far as banning second- and third-trimester abortions.... But the majority — 90% plus — [of] abortions are happening in the first trimester,” Kristan Hawkins, president of Students for Life. “We really have to be making our case to the American people why these abortions are just as equally as gruesome as a later-term abortion.”

Enforcing state laws on medication abortions will likely be more difficult, particularly when the process occurs online.

But abortion rights supporters nevertheless worry about the chilling effect the laws may have on women and on healthcare providers who may believe they have to report suspected abortion cases or face their own legal trouble.

The EMAA Project, a group that advocates for medication abortion care, is having preliminary conversations with the Biden administration on what can be done to bolster access, said the group’s director, Kirsten Moore.

In addition to dropping the in-person dispensing requirement, the FDA has said it will certify pharmacies that want to dispense abortion medication, in line with the FDA’s strict rules that govern its use.

But states that oppose abortion have already indicated they plan to issue their own requirements for certification.

Moore’s concern is that any steps the FDA takes to bolster access to abortion medication under the Biden administration may be undone by a future Republican president. Still, she’s hoping there are small steps that can be taken, such as pressing insurers to cover the drugs, even as the rise of medication abortions takes the legal and political fight into new terrain.

“There is no obvious one, two, three things to solve the problem,” she said. “We’re going to have to be really creative. And it may only be helpful on the margins — which may be important margins.”

This is one in a series of occasional stories about the state of abortion as Roe vs. Wade faces its most serious challenge.