Taking pills to end a pregnancy accounts for a growing share of abortions in the United States, both legal and not. If the Supreme Court overturns Roe v. Wade as expected, medication abortion will play a larger role, especially among women who lose access to abortion clinics.

What is medication abortion?

It’s a regimen of pills that women can take at home, a method increasingly used around the world.

The protocol approved for use in the United States includes two medications. The first one, mifepristone, blocks a hormone called progesterone that is necessary for a pregnancy to continue. The second, misoprostol, brings on uterine contractions.

When can it be used?

The Food and Drug Administration has approved medication abortion for up to 10 weeks of pregnancy. World Health Organization guidelines say it can be used up to 12 weeks at home, and after 12 weeks in a medical office.

Is it effective, and is it safe?

Yes on both counts.

In U.S. studies, the combination of these pills causes a complete abortion in more than 99 percent of patients, and is as safe as the traditional abortion procedure administered by a doctor in a clinic. A variety of research has found that medication abortion has low rates of adverse events, and a recent Lancet study found that patients are generally satisfied with it. Growing evidence from overseas suggests that abortion pills are safe even among women who do not have a doctor to advise them.

“Some people still assume we’re talking about something dangerous or done out of desperation, but increasingly this information is becoming more mainstream,,” said Abigail R.A. Aiken, an associate professor at the University of Texas at Austin who leads a research group there on medication abortion.

Who uses this method?

About half of people who get legal abortions in the United States (and three-quarters in Europe). During the pandemic, medication abortion became more common because patients wanted to avoid going to clinics in person, and a change in federal law made it easier for them to get prescriptions via telemedicine.

It usually comes down to patients’ personal preference, said Dr. Maria Isabel Rodriguez, an associate professor of obstetrics and gynecology at Oregon Health and Sciences University, who has worked on abortion research and policy design. “Some people like surgical, because it’s over with faster, they’re able to have anesthesia, and it’s finished in a defined time,” she said. “Medication can feel more private, some want it at their own home, some say it feels more natural for them, and some say it feels more possible to process a loss.”

Medication abortion is also used by those who live in a place that restricts legal abortion or by those who can’t reach a clinic. The U.S. abortion rate is higher than officially reported by doctors, evidence suggests, because people are ordering pills online. That invisible abortion rate may rise if more states move to ban abortion.

Who prescribes abortion pills?

Doctors with a special registration required by the F.D.A.

But it recently lifted rules that required an in-person appointment. That means more providers are offering medication abortions through telemedicine. The doctor and patient meet online, then the doctor sends pills to the patient’s home through the mail. (Some brick-and-mortar pharmacies have become certified to fill prescriptions for the pills, but this is not yet common.)

New start-ups that specialize in telemedicine abortions, like Hey Jane and Just the Pill, have begun offering the service in states that allow it. But 19 states prohibit pills from being prescribed by telemedicine or delivered via mail. In those places, patients still need to see a doctor in person to pick up the pills. Other states ban medication abortion after a certain number of weeks.

If Roe is overturned, about half of states are expected to ban abortion altogether, and medication abortion is expected to become a legal battleground.

What about pills from overseas?

Online pharmacies overseas sell the pills. An organization called Aid Access offers women in all 50 states advice and prescriptions from European doctors before shipping pills from India. These extralegal channels are becoming more popular as abortion becomes harder to access in some states. After Texas enacted a law in September that banned abortion after about six weeks, requests to Aid Access for abortion pills tripled.

The F.D.A. has asked these groups to stop sales of these medications into the United States, saying they circumvent U.S. drug safety protocols. But researchers who have analyzed the pills in laboratories have found that pills ordered using these services are generally authentic.

The second of the two medications in the official regimen, misoprostol, can also end a pregnancy when used alone. It is around 80 percent effective on its own, although it sometimes has to be taken more than once. That pill is also used to treat ulcers, and is available over the counter in many countries, including Mexico. But the only F.D.A.-approved method in the United States is to use both pills.

Are pills from overseas legal?

No. It is illegal to sell prescription medicine to Americans without a prescription from a doctor licensed in the United States. But enforcement of overseas providers has been uncommon, as it is with other medications Americans order from abroad. And sales would be hard to stop because the medications generally come in unmarked packages in the mail.

“I’m not there, so I don’t have any legal risk,” said Dr. Rebecca Gomperts, the Dutch physician who runs Aid Access, and says she has lawyers advising her, both at home and in the United States. “I know from where I am, I am complying with the law.”

In general, recent state laws do not punish women for obtaining abortions, but have focused enforcement on abortion providers. The exception is older laws in South Carolina, Oklahoma and Nevada. That could change if Roe is overturned and if illicit medication abortions become more common.

“It is not a codified crime to self-manage abortion” in all but those three states, said Farah Diaz-Tello, senior counsel and legal director for If/When/How, a reproductive rights policy and advocacy group. “But it is not lawful for a person to seek prescription medication without a prescription.”

What is the process like?

The first pill, mifepristone, typically has no discernible effect on patients. The second, misoprostol, taken 24 to 48 hours later, causes cramping and bleeding that builds in intensity, Dr. Rodriguez said.

The process lasts about six to eight hours, and is most intense for about one hour. She recommends patients stay home, without other obligations. Ibuprofen and a heating pad are also recommended, because the pain can be strong and the bleeding is much heavier than for a period. After the pregnancy has passed, the cramping and clotting stop, though women generally bleed, similar to a period, for about a week.

In rare cases, less than 1 percent of the time, a patient has heavier-than-expected bleeding and needs medical care. Similarly rarely, the abortion is not complete and needs to be followed up with another dose or a surgical abortion. Women who have these complications can be treated by a doctor with experience treating miscarriages; the symptoms and treatment are the same. Once a medication abortion is begun, it cannot be reversed.