BOSTON — When the end draws near, Dr. Roger Kligler, a retired physician with incurable, metastatic prostate cancer, wants to use a lethal prescription to die peacefully in his sleep. As he fights for the legal right to do that, an influential doctors group in Massachusetts has agreed to stop trying to block the way.

Kligler, who lives in Falmouth, Massachusetts, serves as one of the public faces for the national movement supporting medical aid in dying, which allows terminally ill people who are expected to die within six months to request a doctor’s prescription for medication to end their lives.

Efforts to expand the practice, which is legal in six states and Washington, D.C., have met with powerful resistance from religious groups, disability advocates and the medical establishment.

But in Massachusetts and other states, doctors groups are dropping their opposition — a move that advocates and opponents agree helps pave the way to legalization of physician-assisted death.

The American Medical Association, the dominant voice for doctors nationwide, opposes allowing doctors to prescribe life-ending medications at a patient’s request, calling it “fundamentally incompatible with the physician’s role as healer.”

But in December, the Massachusetts Medical Society became the 10th chapter of the AMA to drop its opposition and take a neutral stance on medical aid in dying.

Most of those changes occurred in the past two years. They proved a pivotal precursor to getting laws passed in California, Colorado and Washington, D.C., said Kim Callinan, chief program officer for Compassion & Choices, an advocacy group that supports legalization efforts around the country. The practice is also legal in Washington, Oregon, Vermont and Montana.

The shifts come as doctors’ views evolve: Fifty-seven percent of U.S. doctors supported medical aid in dying in a 2016 Medscape survey, up from 46 percent in 2010.

Because of the medical society’s vote, Massachusetts is the state most likely to legalize medical aid in dying this year, predicted David Stevens, CEO of the Christian Medical & Dental Associations, a national group of 19,000 health professionals that has opposed such laws in every state.

“I think a neutral stance is probably what’s going to push it over,” he said.

Doctors’ opinions are also playing a role in New York, where the New York State Academy of Family Physicians endorsed an aid-in-dying bill, and the state medical society is surveying its members on the subject.

Efforts to legalize the practice have faced pushback nationally: Last year, lawmakers in 27 states introduced aid-in-dying bills, and none passed. And in Congress, Republican lawmakers have launched several attempts to block the District of Columbia from implementing its law.

This year, Compassion & Choices’ Callinan identified New Jersey, New York and Massachusetts as its top three target states.

Peg Sandeen, executive director of Death With Dignity National Center, an aid-in-dying advocacy group based in Oregon, cited Hawaii as another top target. Advocates there are “trying to break the logjam in the legislature,” where the state Senate passed a bill in March, she said. Hawaii came close to legalizing the practice in 2000.

Massachusetts has been a fraught battleground for the right-to-die movement: In 2012, opponents narrowly defeated a referendum that would have legalized the practice. Home to a robust medical hub and Harvard Medical School, the state is a stronghold for academic medicine.

Kligler, who’s 66, has publicly described his intent to use lethal drugs to die on his own terms rather than endure what he expects to be several months of significant pain, fatigue and declining quality of life.

Kligler said he wants other dying people to have the same option: When he used to serve as a hospice physician to cancer patients, he said, patients used to “ask me to help them to die,” but he had no legal way to do so. Kligler is also suing Massachusetts, arguing that terminally ill patients have a constitutional right to medical aid in dying.

“It’s a question of justice,” Kligler said.

When the Massachusetts Medical Society surveyed members last year, 60 percent said they supported medical aid in dying, and 30 percent said they opposed it.

Dr. Barbara Rockett, a surgeon and past president of the medical society, urged fellow doctors to uphold the group’s long-standing opposition to the practice. Doctors should focus on helping dying patients through hospice and palliative medicine, she said.

“To intentionally help them commit suicide is wrong,” Rockett said. Proponents, meanwhile, say the practice is not “suicide” because the patient is already being killed by a terminal disease.

Rockett said she was disappointed that her fellow delegates in the society voted to adopt a neutral stance.

Even with the doctors group stepping out of the way, the latest aid-in-dying bill, dubbed the Massachusetts End of Life Options Act, faces formidable opposition. Catholic groups, a significant force opposing aid in dying nationally, have a robust base in Massachusetts: Over a third of residents are Catholic, second only to Rhode Island.

Catholic groups provided much of the $5.5 million that opponents spent to defeat Massachusetts’ ballot referendum in 2012, outspending proponents by nearly 5-to-1.

The Boston Archdiocese did not respond to repeated requests for comment for this story. But at the time the referendum failed, a spokesman said the church could not afford to lose on this issue in a Catholic stronghold: “If it passes in Massachusetts,” the spokesman said, “it’s a gateway to the rest of the country.”

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