On Friday, a federal judge in Texas ruled that the Food and Drug Administration didn't properly approve a drug which has been on the market for more than 20 years in the U.S. for medical abortions. The drug in question, mifepristone, is used along with one other drug in most medication abortions in the U.S.

The fallout of the ruling could mean that mifepristone becomes unavailable in the U.S. in the near future, though the ruling is being challenged in court. Depending how legal battles play out and how the FDA responds, the effects of this ruling may apply only in certain states, or may indeed curtail mifepristone use around the country.

If this happens, doctors say they will continue to offer medication abortions without mifepristone, using only the other drug, misoprostol. Here's what to know about how misoprostol-only abortions work, how safe they are and how patients would access them.

How does the single-drug protocol differ from the current standard of care which uses two drugs?

Most medication abortions in the U.S. currently use both mifepristone and misoprostol because patients experience fewer side effects when the medications are combined. A regimen involving both medications is also used for miscarriages.

But misoprostol alone can be used effectively for abortions – and is commonly prescribed in some countries.

"This regimen is still incredibly safe and effective," says Dr. Kristyn Brandi, a New Jersey family planning specialist and spokesperson for the American College of Obstetricians and Gynecologists. "Medication abortion and miscarriage management will not go away with the loss of mifepristone, but it may look a little different."

With the two-drug regimen, patients first take mifepristone – which blocks the hormone progesterone – to end the pregnancy. Patients then take misoprostol 24-48 hours later, which causes the uterus to expel the pregnancy tissue. Patients experience bleeding and cramping, and usually pass the pregnancy within 4-6 hours after taking the misoprostol.

In a misoprostol-alone abortion, patients start the process with misoprostol, using the same amount as is used in the two-drug regimen. Three hours later, they take misoprostol again, causing the uterus to contract. They repeat this for three to four doses until the pregnancy passes, which usually takes between 9-12 hours.

In both cases, patients typically see a doctor or nurse, either in person or online, and then take the drugs at home.

Is the misoprostol-alone regime safe? What can patients expect to experience?

There's lots of research that shows the misoprostol-only protocol is as safe as the two-medication protocol – but it does tend to cause more side effects.

Even though the two-drug protocol is still preferred when possible, there's ample evidence that misoprostol alone is a very effective alternative, according to the Society of Family Planning, an abortion research organization.

Multiple organizations, like the American College of Obstetricians and Gynecologists and the World Health Organization, say the one-medication protocol is an acceptable choice, particularly when mifepristone isn't available.

Patients using misoprostol alone, however, tend to experience more nausea, vomiting, and diarrhea, and a longer duration of cramping and bleeding. That's why it's usually the second choice regimen.

The misoprostol-only protocol is actually faster than the two-medication protocol, which takes about 30 hours total since patients take the second drug at least 24-hours after the first. In the misoprostol-alone regimen, the process usually only takes 9-12 hours, but patients typically experience cramping and bleeding for longer.

When might a patient need to seek further medical help for a medication abortion?

With either regimen, the reasons to seek follow up care are the same.

If patients experience heavy or prolonged bleeding – spotting that persists for over 2 weeks, for example, or bleeding so heavy they soak through more than two pads an hour for over two hours – they might need a procedure to complete the abortion.

A prolonged fever above 100.4 degrees Fahrenheit is also a reason to seek medical care. While low-grade fevers and chills are an expected side effect of misoprostol and aren't life threatening, if a fever persists for more than 24 hours after taking misoprostol, it could be a sign of infection.

Also, if a patient does not experience any bleeding or cramping, the medication may not have worked to end the pregnancy, and she might need more misoprostol or a procedure to have a complete abortion.

How far along into the pregnancy does medication abortion work?

The Food and Drug Administration has approved the two-drug regimen to end pregnancies up to 10 weeks gestational age, but the World Health Organization endorses it up to 12 weeks. After that, they're less likely to be effective and may cause more bleeding and cramping.

For misoprostol-only abortion, it's less clear cut. There's some data showing that the regimen can be effective in ending pregnancies up to 22 weeks. That's according to one study that looked at patients having self-managed abortions, without the direct involvement of a doctor in countries that have had restrictive abortion laws.

But in U.S. states where second trimester abortion is allowed, Brandi says, doctors will typically recommend a procedural abortion in a hospital rather than a medication-based abortion to end pregnancies after 12 weeks. That's because second trimester misoprostol-only abortions can involve more bleeding and prolonged cramping. Doctors would probably only recommend misoprostol-alone in the second trimester in states where patients don't have other legal options.

How do patients get prescriptions for medication abortions? Would they be able to get them for the one-drug regimen?

In states where abortion is legal in the first trimester, patients can speak to a health care provider and get a prescription for medication abortion via telehealth abortion companies, in-person at clinics that provide abortion like Planned Parenthood, and at many general OB/GYN and family medicine clinics.

As long as mifepristone is still available, providers will usually give the two-drug regimen. If it becomes unavailable, many providers have indicated they'd start prescribing misoprostol alone.

Dr. Jamie Phifer, the medical director of Abortion on Demand, says her team is waiting to see how the courts ultimately rule on mifepristone. They will continue to provide mifepristone and misoprostol combination abortions to their patients unless it becomes illegal.

"But we're ready," she adds. "We can make the switch [to misoprostol-only protocols] within hours."

In fact, misoprostol is easier to access than mifepristone. Even before the Texas judge's ruling, mifepristone was subject to special FDA regulations that meant that most commercial pharmacies did not carry it, and patients could only get it at clinics that provide abortions or via pharmacies that had specially registered with the FDA.

Misoprostol, however, isn't subject to these regulations, so it's stocked in almost all pharmacies and hospitals.

Are patients able to get the medication in states where abortion is banned?

Neither the two-drug regime, nor misoprostol-alone medication abortions are available legally in these states. Misoprostol itself remains legal when used for other purposes, like treating ulcers or inducing labor.

However, there are a number of services that help patients in these states access abortion pills.

For instance, Mayday.Health offers step-by-step instructions for setting up a mail-forwarding address, so patients can list an address in a permissive state on their intake forms for a telehealth abortion, then get the pills sent along to an additional address somewhere else. Plan C is a website that provides up-to-date information about how to get abortion pills at home.

The Miscarriage and Abortion Hotline offers free consultations with clinicians if a patient has questions about a medication abortion, even if she had the abortion in a state where it's illegal.

Other organizations openly flout the law to provide abortion medications in all 50 states.

Aid Access, for example, is based in the Netherlands and will mail mifepristone and misoprostol to patients in states where abortion is banned. Pills sent from abroad are not subject to FDA approval and safety regulations. The organization also employs U.S.-based health care providers, who prescribe FDA-regulated abortion pills via telehealth in states where it's allowed.

Mara Gordon is a family physician in Camden, N.J., and a contributor to NPR. She's on Twitter at @MaraGordonMD.