Rosenberg has raised the prospect of lawmakers sharply increasing the marijuana tax rate , lowering the 12-plant-per-household limit on homegrowing pot, and even raising the legal age for purchase, possession, and use up from 21.

Public comments from Senate President Stanley C. Rosenberg about potential changes are setting off alarm bells among backers.

Marijuana legalization advocates fear the Massachusetts Legislature, which has already delayed the opening of pot shops, will now gut several key parts of the law approved by 1.8 million voters in November.

Rosenberg supported legalization and said he will respect the will of the voters, but believes the law needs refinement. He has not taken firm positions on those specific changes. In public forums, however, he has said they are likely to be part of the debate over fine-tuning the law.


But even the specter of legislators meddling is giving advocates agita.

“The idea that legislators in my state could eviscerate a popular ballot question, as I watch a minority of conservative voters overrule the majority of national voters, I’ll be damned if I’m going to sit still,” said Michael Cutler, a Northampton lawyer who helped write the initiative.

The prospect of changes to the tax rate, homegrow limit, and legal age “sound to me like fear and stigma and ignorance, unless the legislators promoting changes have some evidence — which I haven’t heard them identify yet,” he said.

Cutler pointed out that the majority of cities and towns voted for legalization (overall, the vote was 54 percent to 46 percent ), and that legislators would have their voters to answer to for any changes.

“People like Senate President Rosenberg, whose hometown voted for this ballot question at a 75 percent rate, need to talk to their constituents,” Cutler said of the Amherst Democrat.

Jim Borghesani, a leader of the initiative, who currently represents the national Marijuana Policy Project in Massachusetts, decried “the headlong rush by legislators to alter Question 4 without any expert guidance, without any solid data, and without any acknowledgment that the system is designed to be regulated, not legislated.” He called that prospect “extremely troubling.”


Dick Evans, a key legalization advocate in the state for almost 40 years, said the changes the Legislature is “talking about making to the law constitute a solution in search of a problem.”

The Legislature may take up other changes as well: restrictions on pot-infused edibles like candy and cookies; a legal standard for driving under the influence (there’s currently no marijuana impairment standard in the law comparable to the 0.08 percent blood alcohol concentration cut-off for alcohol); efforts to give cities and towns more control over pot shops; and creating public health and education campaigns to enlighten residents about the newly legal drug.

Despite advocates’ dismay at his public comments, Rosenberg has been the highest-ranking politician to support legalization. He’s met with advocates and people in the marijuana business world multiple times.

“When I met with the advocates in my office,” he said in a statement to the Globe, “I assured them that the Legislature will respect the will of the voters who legalized recreational marijuana on Nov. 8.”

In the statement, Rosenberg said that lawmakers will engage people with a stake in the industry in a “robust, inclusive, and deliberative process” to address issues that have come up in other legalization states.


For example, in a recent radio interview on WCAP Rosenberg said, “It’s legal now to have 12 plants in your home, but the advocates understand that this is likely to be debated in the process,”

There are coherent reasons why legislators might want to make changes advocates fear.

■ A 12-plant-per-household homegrow limit is risky, officials in other legalization states say, because it could create a gray market in which people grow plants legally, then illegally sell the pot — which won’t be tested, taxed, or overseen by state authorities. If the growers know what they are doing, 12 plants could provide much more marijuana than a standard household would be able to consume.

■ The Massachusetts law sets a tax rate for retail sales, 3.75 percent, much lower than other legalization states — Washington State imposes a 37 percent tax on pot, for example. That, legalization opponents fear, won’t be enough to pay for the oversight needed for the new industry, nor to support related services like addiction counseling. (Cities and towns can add another 2 percent local pot tax, and marijuana will also be subject to the state’s 6.25 percent sales tax.)

■ Raising the legal age, while unlikely, is supported by some scientific data. Rosenberg said this month he feels obligated to put the idea on the table. That’s because “smoking marijuana, especially in substantial quantities for people under the age of 25, has a potentially bad effect on the development and formation of the brain because . . . it’s not fully developed, until about age 25.” (Dr. Sharon Levy, an expert in adolescent substance abuse at Boston Children’s Hospital, said Rosenberg is essentially correct. “Until that last stage of development is complete, the brain is more configured in a way that’s set for learning than real proficiency,” she said. “Marijuana use can interrupt some of that growth and development.”)


But advocates say the law Massachusetts voters backed was carefully written with public health and safety in mind. They say lawmakers ought to refrain from making any changes until the state’s new pot regulatory body, the Cannabis Control Commission, has a chance to write regulations.

Further, they argue, the tax rate is sufficient for the administration of a regulatory system, and a higher rate would invite a continuation of the black market because consumers would go looking for cheaper pot. They say the homegrow limits won’t have the negative effects opponents fear. And they note that the legal age matches that of alcohol, and a higher one would invite continued black market activity.

Finally, they say it’s undemocratic to unwind key parts of a law so many people voted for.

In December, with just a few legislators present, the Senate and House passed a bill delaying the likely opening date of retail marijuana shops from January to July 2018. Governor Charlie Baker, a Republican who campaigned against legalization, signed that legislation into law.

House Speaker Robert A. DeLeo, a Democrat and legalization opponent, and Baker have both affirmed they will respect the will of the voters, but said they are open to making changes to the law.


Rosenberg and DeLeo are forming a joint Senate-House committee on marijuana. That group is poised to hold hearings and conduct research before coming up with new laws relating to marijuana legalization.