Former Republican House Speaker John Boehner will join the board of directors of a marijuana holdings corporation, saying his views on the substance have "evolved."

Acreage Holdings, which describes itself as "one of the nation's largest, multi-state actively-managed cannabis corporations," announced Wednesday that the former U.S. representative from Ohio has joined its board of advisors, and will join the board of directors once it is formed.

In a statement sent to CNBC, Boehner said his thinking on cannabis "like that of millions of other Americans, has evolved as I've learned more about the issue."

"I decided to get involved because of the struggles of our country's veterans and the opioid epidemic, after learning how descheduling the drug can potentially help with both crises," he said.

Boehner explained that the federal government should stop labeling cannabis a "schedule 1" drug — lumping it in with heroin and cocaine as having the highest potential for abuse.

"Descheduling will reduce the conflict between federal policy and state programs" which have pursued more lenient policies on marijuana under the 10th Amendment to the U.S. constitution, he said.

Former Massachusetts Gov. Bill Weld, a Republican who ran on the Libertarian Party ticket alongside former New Mexico Gov. Gary Johnson in the 2016 presidential election, is also joining Acreage's board.

Boehner was the top Republican in Congress from 2011 through 2015. He was succeeded by Paul Ryan, R-Wis., who announced Wednesday that he will not seek re-election at the end of his current term.

Boehner has been a vocal critic of President Donald Trump's administration, as well as many of his former colleagues in the House, since his retirement. As Boehner marks his self-described evolution on marijuana, which is used both as a recreational and medical drug, Attorney General Jeff Sessions has taken steps to pursue enforcement against marijuana more aggressively than the Obama administration.

In a joint statement, Boehner and Weld argued against marijuana's continued federal status as a schedule 1 drug.

The "negative implications" of the schedule 1 label include "the lack of research, the ambiguity around financial services and the refusal of the VA to offer it as an alternative to the harmful opioids that are ravishing our communities," the former politicians said in the statement.

Boehner announced his new affiliation in a tweet on Wednesday.

Boehner tweet

Acreage Holdings' CEO, Kevin Murphy, said Boehner and Weld "have shaped the political course of our country for decades and now they will help shape the course of this nascent but ascendant industry."

While Boehner once took a hard-line position against legalizing marijuana, he has maintained an infamous two-pack-a-day tobacco smoking habit for years.

A spokesman for Boehner did not immediately respond to CNBC's request for comment.

Correction: Gary Johnson is a former governor of New Mexico. An earlier version misstated his state and status.