The mayors of Boston and Cambridge head to Canada next week to tour facilities where doctors and nurses are on hand while patients inject illegal drugs.

There are no such supervised injection sites in the United States, although a handful of cities battling the drug overdose epidemic are in the planning stages.

A state commission looking into whether Massachusetts should allow such facilities heard a resounding yes on Wednesday from medical and legal experts, beginning with Dr. Jessie Gaeta, chief medical officer at the Boston Health Care for the Homeless Program.

Gaeta cataloged 109 studies on supervised injection sites for the state's Harm Reduction Commission, a group looking at ways to slow overdoses and deaths during the opioid and broader drug epidemic. Gaeta says all the studies find benefits.

"There’s more than enough evidence now that we should be adopting this model," Gaeta said.

Most of the research Gaeta presented is based on the oldest supervised injection facility (SIF) in North America, Insite, which opened in Vancouver in 2003. One widely cited study shows drug users within close proximity to the clinic were 35 percent less likely to die after an overdose. Another found Insite clients were 33 percent more likely to enroll in treatment than other drug users in Vancouver. Treatment rates rose to 54 percent for those who met with a counselor while at Insite.

Researchers at Johns Hopkins found that Insite saved $4.35 for every dollar spent because it prevented HIV, hepatitis C, hospital visits and deaths. The number of people injecting drugs and leaving needles on the streets around Insite dropped after the clinic opened. Studies have not found that supervised injection sites encourage people to begin using drugs or attract drug dealers, although this research is more than 10 years old.

Gaeta told the commission there's no need to start with a pilot clinic, which was proposed during the last legislative session. Massachusetts should open clinics now.

"There’s no question, we should be implementing supervised consumption," Gaeta said.

A closer look at the research is giving former opponents a reason to rethink their position on SIFs.

"I went from a hard no on safe injection sites to, am I in the right place on that?" Walsh said after the meeting. "We have to look at it all. This is an epidemic. If we want to really combat that in the next 20 years, we have to really take different approaches and this potentially could be one of those approaches."

Boston Mayor Marty Walsh in November 2018 (Jesse Costa/WBUR)

Walsh says he's especially impressed by the study that shows Insite leads to treatment.

"That alone, potentially, is worth exploring," Walsh said.

Gov. Charlie Baker’s representative, commission chair Marylou Sudders, said she’s reviewing the literature and is concerned that some of it is from an earlier stage in the epidemic, before fentanyl. Sudders added that she didn’t see evidence of that Insite is a path to treatment during a visit to Vancouver last year but the clinic's record of zero fatalities is impressive.

"One of the things I continue to be reminded of is that no one dies within a safe consumption site," said Sudders, Baker's secretary for health and human services. "But there are still a lot of issues for the commission to deliberate before I settle on where I come down on this."

One big issue is whether such clinics would be allowed to operate anywhere in the U.S. A nonprofit in Philadelphia plans to open a supervised injection site later this year even though Department of Justice leaders have said they would move quickly to shut it down.

U.S. Attorney for Massachusetts Andrew Lelling was not available to comment for this story. A spokeswoman said a statement issued in July 2018 stands.

"Providing a sanctuary to accommodate risky and lethal illegal drug use undermines all of the hard work of treatment providers and law enforcement across the Commonwealth," said Lelling, in that statement.

But Northeastern University law professor Leo Beletsky outlined a path for the commission to legal operation of a SIF in Massachusetts. It includes changing state drug laws to protect clinic staff and challenging any federal intervention in court. Beletsky advised commissioners that a government run clinic could argue that saving lives during a state declared public health emergency takes per is a higher priority than enforcing federal drug laws.

Beletsky told the commission that threats from federal prosecutors are driven by current political winds, not public health.

"It’s basically a matter of politics to determine how prosecutorial discretion would be used against these facilities," Beletsky said.

Beletsky pointed out that federal prosecutors made similar threats about cracking down on marijuana dispensaries in Massachusetts and didn't follow through. Dispensaries violate more federal laws than would a SIF, Beletsky said, because staff possess and sell marijuana. Both marijuana and heroin are both schedule I illegal drug under federal law. Fentanyl is schedule II, considered less open for misuse.

Attorneys for Boston and Cambridge are looking at the legal risks for opening a SIF. Cambridge Mayor Marc McGovern says he’s convinced his city should open one.

"If we can create a space where people who are using dangerous drugs can do so and live so they can access treatment at another point, then we are doing something very important," McGovern said. "We have to think boldly if we’re really going to do something meaningful to save people’s lives."

But with the federal threats, could Cambridge or Boston find doctors and nurses to staff a supervised injection clinic? Gaeta says she would take the chance because she’s desperate for an option that doesn't include finding patients turning blue on a bathroom floor. She revived three patients in the last five days.

"I know that there are people dying because they are alone when they inject, I’m watching it happen," Gaeta said. "So I far haven’t lost someone, bu we've come really close. That’s the reason I feel desperate."

Supervised injection sites aren’t the only measure the commission is reviewing. The list includes greater access to naloxone, more needle exchanges, expanding medication-assisted treatment in prisons and at least one more highly controversial option: prescribing heroin to long-term users to make sure they aren’t getting fentanyl.