The Food and Drug Administration has changed its guidelines for use of the abortion pill, potentially increasing access to a method of pregnancy termination that has been heavily restricted in some states.

The changes bring the guidelines in line with what many doctors consider standard practice. They also undercut one strategy that had been used by antiabortion activists to reduce access to medication-induced abortion, which women are increasingly using as an alternative to the surgical procedure.

The new label lowers the recommended dosage of one of the two drugs used in medication abortions and allows the treatment to be used up to 70 days into pregnancy — three weeks longer than the previous guidelines. It also relaxes prescriber guidelines to allow, for example, a nurse practitioner to administer the drugs.

In practice, the situation will not change for most of those seeking abortions, as doctors for years have been diverging from the old FDA protocol on the basis of new research — a common practice known as prescribing a drug “off-label.”

But a handful of states have laws requiring abortion providers to adhere at least in part to the FDA-approved label, leading some providers to all but abandon the use of the abortion pill.

“The label change for medication abortion will mean that it will once again be a real option for Preterm’s patients and women across the state,” said Chrisse France, executive director of Preterm, the largest abortion clinic in Ohio. “We will no longer be forced to practice medicine mandated by politicians whose ultimate goal is to shut us down.”

In 2011, when Ohio passed a law requiring clinics to adhere to the FDA protocol, requests for medication abortions at Preterm plummeted from about 13 percent of patients to fewer than 2 percent, France said in a teleconference Wednesday with reporters. Reverting to the old protocol made abortions costlier and required four visits to the clinic, France said. Surgical abortions in Ohio typically require only two visits, she said.

Texas and North Dakota also have laws requiring abortion providers to follow FDA guidelines, according to the Guttmacher Institute, which studies reproductive rights issues. Arizona and Arkansas passed such laws, but they have been temporarily blocked by the courts.

Groups said the new label guidelines could lead to more medication abortions nationally. More doctors may be persuaded to allow the use of the abortion pill later in pregnancy than they had previously been inclined to do, they said, and more nurse practitioners could be empowered to administer the drugs. Medication abortions accounted for nearly 1 in 4 nonhospital abortions in 2011, the latest year for which figures are available, according to Guttmacher.

Mark S. DeFrancesco, president of the American Congress of Obstetricians and Gynecologists, issued a statement Wednesday saying that he was “pleased that the updated FDA-approved regimen for mifepristone reflects the current available scientific evidence and best practices.”

Antiabortion groups noted that the new label carries over the old label’s warnings — including the rare possibility of infection or death.

“The new label affirms the deadly realities of chemical abortion and underscores the need for in-person patient examination and follow-up care as well as the fact that the abortion drug regimen presents serious risks to women’s health,” Anna Paprocki, staff attorney for Americans United for Life, said in a statement.

The label change, effective immediately, applies to Mifeprex, the brand name for mifepristone, the costlier of the two drugs used. It blocks the production of progesterone, a hormone that prepares the lining of the uterus for a fertilized egg. A day or two after taking that drug, the woman takes the second drug, misoprostol, which causes the uterus to contract and expel the pregnancy.

Most clinics price surgical and medication abortions similarly, said Vicki Saporta, president of the National Abortion Federation, a trade group for abortion providers, so a reduction in the Mifeprex dosage may reduce the overall cost of the procedure.

The FDA declined to make any officials available for interviews, saying it did not want to identify individuals involved in the Mifeprex decision because of concerns they might be targeted for harm by people opposed to the use of the abortion pill.