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Denver's mile-high reputation could get another boost after psychedelic drug advocates received the green light Friday to put an initiative before city voters to decriminalize magic mushrooms.

The Denver Psilocybin Mushroom Decriminalization Initiative will ask voters in May to approve an ordinance that would make possession of the drug, no matter the weight, legal for those 21 and older. They could also grow it. The proposed law, however, would not legalize retail sales, which have made the city an international darling of the cannabis world.

After reviewing signatures submitted by the Denver Psilocybin Mushroom Decriminalization Initiative it has been determined that they submitted a sufficient number of valid signatures and the question will appear on the May 7, 2019 Municipal Election ballot. #DenverVotes — Denver Elections (@DenverElections) February 1, 2019

The city's Elections Division said organizers turned in enough valid signatures to qualify for the May 7 municipal ballot. Kevin Matthews, director of the initiative campaign, said it will be the first time psilocybin decriminalization has come before U.S. voters.

He said the campaign's long-term goals are to educate the public on the drug and stop putting users behind bars.

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"I don't foresee a recreational cannabis model in the near future," he said.

The measure seeks to put the brakes on criminal penalties for use and possession of psilocybin mushrooms. Its no-limit component results from mushrooms' nature as a heavy, wet fungus that is then dried out, Matthews said. Proponents say prosecutors don't always recognize the difference, but law enforcement is evolving.

"We’re a pretty progressive city when it comes to drug policy," Matthews said, referring to the Denver's mid-2000s marijuana decriminalization and to the state's legal recreational sales that started in 2014.

"In some ways marijuana did open the door," he said.

Matthew W. Johnson, a psychiatry and behavioral sciences professor at Johns Hopkins University School of Medicine, has researched psilocybin for possible use in treating anxiety and depression in cancer patients.

He said in an NBC News interview in June that the prospect of unfettered access to the drug conjures "real concerns about very real risks of psychotic disorders — what people refer to as a bad trip."

"I speak firsthand to how intense these experiences can be," he said.

UCLA psychiatry professor Charles Grob, who has also researched the drug, seemed to agree.

"If, in fact, it’s ever available on a mass basis, it would be imperative to have a strong education component so people could understand what these compounds are," he said in a separate June interview. "They should not be treated in a trivial manner."

Matthews says he's moving forward with a clear mind and plans a long-term education and research strategy that includes a mayoral panel empowered by the initiative and tasked with reviewing its impacts.

"This is going to be a work in progress," he said.