John Boehner, the speaker of the House from 2011 to 2015, reversed a long-held stance against marijuana legalization on Wednesday, saying on Twitter that “my thinking on cannabis has evolved.”
Mr. Boehner, a Republican leader who in 2011 told a constituent he was “unalterably opposed” to legalization, joined the board of advisers of Acreage Holdings, a cannabis corporation that operates in 11 states.
While the announcement might be viewed as a sign that cannabis is becoming a big business that can afford to ally with prominent names from the world of politics, Mr. Boehner cast it as a genuine change of heart.
In a statement, he and William F. Weld, the former Massachusetts governor, who also joined the Acreage Holdings board, said “the time has come for serious consideration of a shift in federal marijuana policy.”
“I’m convinced de-scheduling the drug is needed so we can do research, help our veterans, and reverse the opioid epidemic ravaging our communities,” Mr. Boehner wrote on Twitter, referring to how the federal government classifies marijuana.
The statement was no surprise in the case of Mr. Weld, a supporter of legalization who ran on the Libertarian Party’s ticket in 2016 with Gary Johnson, a former New Mexico governor.
But it was a dramatic U-turn for Mr. Boehner, of Ohio, who had been considered no friend of marijuana advocates while in office. His only vote on legalization came in 1999, when he voted to prohibit medical marijuana in Washington.
Erik Altieri, the executive director of the National Organization for the Reform of Marijuana Laws, a pro-marijuana advocacy organization, said Mr. Boehner had opposed “even the mildest of marijuana law reforms.”
“He’s really just a sign of the times in terms of where the American public is going,” Mr. Altieri said.
About 61 percent of Americans said marijuana should be legalized in a Pew Research Center survey from October, compared with 31 percent in 2000. A Gallup poll from October revealed similar results, with 64 percent saying they supported legalization.
But there remains a stark partisan divide. While 69 percent of Democrats supported legalization in the Pew survey, just 43 percent of Republicans did. In the Gallup poll, 72 percent of Democrats supported legal marijuana, compared with 51 percent of Republicans.
Mr. Altieri said Mr. Boehner could have more credibility among opponents, able to meet them where they are. And he said it would be crucial for Republican leaders to take charge of the issue, considering the party’s control of the federal government and numerous state capitols.
“If this is only led by Democrats, we will continue to see no forward momentum on this issue,” he said. “We really need to present this as the bipartisan issue it really is.”
In an interview with Bloomberg, Mr. Boehner said he began to shift his opinion after seeing marijuana help a close friend deal with back pain. He said “you begin to really scratch your head” when looking at how many people are in prison for marijuana possession.
“Over the last 10 or 15 years, the American people’s attitudes have changed dramatically,” he said. “I find myself in that same position.”
While marijuana advocates largely welcomed Mr. Boehner’s support, some hadn’t forgotten his history of opposition.
Morgan Fox, a spokesman for the Marijuana Policy Project, a group that supports legalization, said Mr. Boehner “should be actively working to reform federal marijuana laws to allow states to determine their own policies, rather than just consulting with a business to navigate the conflicts between state and federal law.”
“His positions on the issue while in House leadership most likely slowed progress for marijuana reform legislation,” Mr. Fox said, “and he owes it to anyone whose life has been negatively impacted by a marijuana arrest to use his considerable influence to make up for that.”