Two marijuana legalization campaigns have joined forces, ending the possibility of competing measures on the 2016 ballot that advocates say could have split the vote.

The Campaign to Regulate Marijuana Like Alcohol, an effort backed by the Marijuana Policy Project, announced Monday that it will stop collecting signatures to support the initiative it filed in March that would set up a system to regulate and tax the sale of marijuana to adults. The group will keep its name but will now spearhead the campaign in support of a similar initiative filed in February by Legalize Maine, which billed itself as a homegrown group supported by people in the state’s agriculture and medical marijuana industries.

The development ends the fragmentation among supporters of legalization that made the movement vulnerable, and it also eliminates the possibility that voters would pass two legalization questions, which would have forced the legalization language into the hands of the Legislature.

While advocates say they’re confident Maine is ready for legalized marijuana, they also were concerned that having two similar proposals on the ballot would have created confusion among voters. If both qualified for the ballot and were approved, the Legislature would have had the messy job of sorting out the conflicts with statute.

“We’ve all been concerned about having two initiatives and splitting the vote,” said state Rep. Diane Russell, D-Portland, a longtime legalization advocate who has supported the Campaign to Regulate Marijuana Like Alcohol. “I think when it comes down to it, the people of Maine support legalizing marijuana in a responsible, safe manner. There would have been confusion about which one to support.”

There was tension from the start between Legalize Maine and the Campaign to Regulate Marijuana Like Alcohol. Before launching their separate initiatives last winter, the groups met but were unable to agree on details, including the amount of marijuana adults 21 and older would be allowed to possess. The Legalize Maine proposal, which now is being backed by both groups, sets a possession limit of 2.5 ounces, while the other initiative capped the amount at 1 ounce. The Legalize Maine campaign pushed its initiative as the best fit for Maine because it was not backed by a national organization that it said takes a one-size-fits-all approach to marijuana legalization policy.

David Boyer, campaign manager for the Campaign to Regulate Marijuana Like Alcohol, said it became clear as signatures were collected that “folks were confused as to why there were two initiatives that both made marijuana legal and were very similar.”

“Joining forces is the best step forward, not only for our respective campaigns, but for Maine as a whole,” Boyer said. “We all agree marijuana prohibition has been a colossal failure and that it must be replaced with a system in which marijuana is legal for adults and regulated like alcohol. We can more effectively accomplish our shared goal by combining resources and working together instead of on parallel tracks.”

Paul McCarrier, president of Legalize Maine, said in a prepared statement that the joining of the campaigns was “a major milestone in the path to ending marijuana prohibition in Maine.”

“Either of these campaigns could be successful on their own, but together we can put our best feet forward in 2016,” he said. “Both campaigns have done a great job of educating voters, organizing volunteers and raising funds, and now we can ramp up those efforts even more.”

McCarrier referred all questions to Boyer and said he would no longer speak with the media about the initiative and campaign.

Scott Gagnon, director of Smart Approaches to Marijuana Maine, a group formed to fight legalization, isn’t surprised the two legalization campaigns chose to combine efforts, saying each group would have trouble getting enough signatures to qualify for the ballot. He called the move “a clear signal that there is no appetite in Maine to legalize and increase access to an addictive substance.”

“Maine is experiencing a significant substance abuse epidemic statewide,” he said. “I think Mainers understand that our young people do not start their substance abuse with heroin. They experiment with drugs like tobacco, alcohol and, increasingly, marijuana. … It is an absolutely tone-deaf policy proposal to create another legal, addictive drug industry while we are in the middle of this crisis.”

Each campaign had collected about 40,000 signatures. The groups now will work on collecting the roughly 21,000 additional signatures needed to qualify the Legalize Maine initiative for the November 2016 ballot. The petition must be filed with the secretary of state by Feb. 1.

Legalize Maine has raised more than $92,000 this year, according to its most recent campaign finance report. During the same period, the Campaign to Regulate Marijuana Like Alcohol raised just over $106,000. Both campaigns reported that most of their expenditures from July through September went to paying signature collectors.

The Campaign to Regulate Marijuana Like Alcohol is backed by the Marijuana Policy Project, a national group based in Washington, D.C., that led successful efforts to legalize recreational marijuana use in other states, including Colorado. The Marijuana Policy Project operates on an annual budget of around $3 million.

Maine has allowed medicinal marijuana use since 1999. If the state legalizes recreational marijuana, it will join a small number of Western states that allow adults to buy and possess the drug. Colorado, Washington, Oregon, Alaska and Washington, D.C., have passed laws legalizing recreational pot despite the federal prohibition.

A poll in the spring of 2015 by Critical Insights, a Portland market research firm, found that 65 percent of Mainers support legalizing marijuana. If it is legalized, 79 percent of people believe it should only be sold in licensed establishments, according to the poll. A new Gallup poll released this month shows 58 percent of adults in the United States think pot should be legal, up from 51 percent in October 2014.