Senate President Stanley C. Rosenberg said Thursday he will vote to legalize marijuana for recreational use, becoming the highest-ranking state official to back the November referendum, and putting him at odds with the majority of Beacon Hill lawmakers who vociferously oppose the measure.
“I’m going to vote for this ballot question,” the Amherst Democrat said on WGBH-FM.
His new position comes after more than a year of declining to take a stance on Question 4, which would eliminate penalties for possessing, using, or purchasing marijuana on Dec. 15, and would allow recreational pot shops to open in 2018.
The two other top Beacon Hill officials, Republican Governor Charlie Baker and Democratic House Speaker Robert A. DeLeo, are working with Mayor Martin J. Walsh of Boston to defeat the referendum. They frame their opposition to the measure through the lens of the deadly opioid overdose scourge in the state.
Opponents also worry about a billion-dollar pot industry taking advantage of the vulnerable and putting profits ahead of public health and safety.
Rosenberg, a liberal rooted in a philosophy of letting people do what they want unless they are hurting someone else, said he would work “to improve” the proposed legalization law, should voters greenlight it.
In the radio interview with Margery Eagan, Rosenberg said the Legislature is “going to have to go in and work on that bill, once it’s approved by the voters.”
While a law passed by voters is the same as any other statute — lawmakers can tinker with it as they see fit — legislators are often reticent to monkey with the will of the voters.
But speaking to the Globe later Thursday, Rosenberg said any changes to the measure, should it pass, would be focused “on public health and public safety — trying to improve what’s already there.”
The longtime legislator said he is “of the school that we have to respect the will of the voters, but the voters are voting in principle, not on every detail of the bill.”
Aspects of the bill he floated “perfecting” included:
■The tax rate — which many opponents worry is too low to fully fund enforcement of and education about the new industry;
■Requirements regarding marijuana-infused products, “edibles and beverage and salves and creams and things of that nature,” which officials say pose unique challenges that marijuana plant matter does not;
■Education about and treatment for marijuana addiction;
■And a framework on drugged driving, which “other states have struggled with” (Massachusetts law doesn’t have a marijuana impairment standard like it does for alcohol — 0.08 or greater blood alcohol concentration).
The pro-legalization YES on 4 campaign said that Rosenberg deserves “enormous credit for taking a courageous stand on replacing the failed system we have today with a regulated structure that will actually control marijuana in Massachusetts and generate much-needed revenue for taxpayers.”
But he is out of step with his colleagues. One-hundred nineteen state senators and representatives oppose the measure, according to the Campaign for a Safe and Healthy Massachusetts, the ballot committee fighting against legalization.
Advocates for legalization in Massachusetts say their antagonists are “prohibitionists” mired in the past. They say legalization will end more than a century of failed attempts to stop pot use, which has ensnared otherwise law-abiding citizens in the criminal justice system. And they insist moving sales from criminals in back allies to regulated stores that check IDs and pay taxes is the smart move.Joshua Miller can be reached at firstname.lastname@example.org. Follow him on Twitter @jm_bos and subscribe to his weekday e-mail update on politics at bostonglobe.com/politicalhappyhour