Massachusetts legislators reached a deal to advance a long-debated bill focused on preventing opioid overdose deaths and improving access to treatment while omitting one central sticking point: a proposal to allow overdose prevention centers.

The House passed a version of the bill in June, and the Senate responded with a version in July that included the provision that would allow cities and towns to locally approve overdose prevention centers, or safe consumption sites, where people can use drugs under the supervision of trained medical staff.

Some advocates for people who use drugs and substance use experts argue that, while the compromise allows other important provisions to move forward, it represents another defeat in a years-long fight to legalize an important tool in overdose prevention.

The latest version of the bill, filed Tuesday, includes proposals to mandate insurance coverage for overdose-reversing drugs like Narcan, eases access to those reversal drugs, and requires the state to close a court-ordered treatment program that channels incarcerated men into substance use treatment.

Dr. Andrew Kolodny, medical director for the Opioid Policy Research Collaborative at Brandeis University’s Heller School, says he would like to see a pilot program launched in Boston — but that he doesn’t see the evidence as conclusive on overdose prevention centers.

Many advocates, though, were more frustrated with lawmakers when asked about the proposal’s exclusion.

“It’s an act of political cowardice,” said Cassie Hurd, the executive director of the Material Aid and Advocacy Program and the co-founder of safe consumption site advocacy organization SIFMA-Now!. “It’s really shameful that we’re compromising on people’s lives.”

“Absolutely there are important elements of the substance use disorder bill that has moved forward,” Hurd said, “but ultimately we know that there are few interventions that have proven to be as effective at reducing overdose deaths than overdose prevention centers.”

Six years ago, Senate leaders advocated for an overdose prevention center pilot program, a measure that was eventually removed from a similar bill after pushback from state leaders, including then-Gov. Charlie Baker.

Kolodny considers any progress towards easing access to opioid treatment — especially medications like buprenorphine or methadone — as a higher priority.

“There are different innovative approaches that I think we should be trying, but a lot of these approaches are sort of the gravy, and we’re still missing the meat,” Kolodny said. “For us to have an epidemic of people with a life-threatening condition, they should be able to walk into any health care facility and immediately access treatment.”

Deaths from opioid-related overdoses fell by 10% between 2022 and 2023, the most significant decline in more than a decade, with 2,125 deaths recorded for that year, according to state data. Boston was the outlier in a statewide decline, with the highest number of overdose deaths in seven years, and statewide numbers still represented the third-highest rate since 2001.

In 2023, the state Department of Public Health released a report recommending the legalization of overdose prevention sites and cited 70% support among the public, according to a poll conducted by Massachusetts for Overdose Prevention Centers and Beacon Research.

Overdose prevention centers, which have existed for decades in Canada, Australia and Europe, are still illegal under federal law. New York opened the first publicly recognized overdose prevention site in 2021, and the first such facility in New England had a ribbon-cutting ceremony this month in Providence, Rhode Island.

“We like to consider ourselves leaders here in the commonwealth, but Massachusetts really is far behind in supporting people who use drugs,” Hurd said. “Legislators are ignoring that people deserve access to resources and support that will keep them as healthy as possible.”

While New York and Providence are not perfect comparisons for Boston in size or need, “we don’t know unless we try,” Hurd said.

Azzy-Mae Ní Mháille, who represents advocacy organization ACT UP Boston and the Eastern branch of the New England Users Union, a local advocacy group for people who use drugs, says harm reduction tools like the distribution of tests and overdose prevention centers are ways to reduce the already-existing risk of overdose death or the spread of diseases that can be transferred from unsafe supplies.

“We already do have supervised consumption spaces, we call them bars,” Ní Mháille said. “We already have commonsense solutions in play, we just refuse to use them for stigmatized substances.”

Offering spaces where drugs of any kind are regulated and users are supervised would reduce the dangers associated with taking those drugs, Ní Mháille said.

“People who use drugs are going to consume substances,” they said, “with our permission or without our permission.”

The House is expected to take up the bill on Thursday, and it could arrive on Gov. Maura Healey’s desk just before the legislative session ends on Dec. 31.