Campaign manager for the Denver Psilocybin Initiative Kevin Matthews wears a mushroom necklace at a May 7 election-watch party for the first ordinance in the nation decriminalizing psilocybin mushrooms. (Michael Ciaglo/Getty Images)

Reilly Capps lives in Denver and is the drugs reporter for Rooster magazine.

DENVER – Voters in Denver made history May 7 as the city became the first in the nation to approve an ordinance decriminalizing a psychedelic — psilocybin mushrooms, or “shrooms” — that many thought had disappeared decades ago along with tie-dye and love-ins.

The surprise win for Initiative 301 came by a razor-thin margin, 50.6 percent to 49.4 percent, with 176,000 votes cast. But it was also familiar territory for Colorado’s biggest city, which pioneered the decriminalization of marijuana in 2005, in a development that later spread across much of the country.

Psilocybin, one of the active ingredients in “magic” mushrooms, is illegal in most of the world, although it is tolerated in a few places, including Jamaica and Brazil.

To be clear, shrooms will not be fully legal here. They will be treated the way marijuana was in Denver after decriminalization in 2005: city cops’ and the district attorney’s “lowest law enforcement priority.” The new ordnance specifies that no city funds are to be used to jail, arrest or even ticket someone for possession of hallucinogenic mushrooms — if the person is over 21 and says the shrooms are for personal use.

Selling, even among friends, will remain a crime. No shroom stores, unlike the many marijuana shops that have flourished in Denver since the state voted to legalize recreational pot in 2012.

But, like the gradual loosening of marijuana laws, Denver's city-level change to a police policy for psilocybin mushrooms may reflect a shifting view of that drug.

Mexican Indians for centuries regarded magic mushrooms as mysteriously potent, both for spiritual and medical purposes. Scientists in the modern era have periodically investigated psilocybin’s potential as a treatment for maladies such as addiction and depression, coming away with promising results.

A 2006 Johns Hopkins University study, titled “Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual significance,” found that a third of participants said a psilocybin trip was the most spiritually significant experience of their lives.

Some health risks are associated with psilocybin. A 2016 Johns Hopkins survey of nearly 2,000 mushroom users asked if they’d had “bad trips.” Of those who had, about 40 percent said their bad trip was among the top five most challenging experiences of their lives; 11 percent said they put themselves or others at risk of physical harm; and 8 percent sought treatment for “enduring psychological symptoms.”

One of the biggest boosts for psilocybin came last fall when the Food and Drug Administration declared psilocybin-assisted psychotherapy a “breakthrough therapy” for depression. The agency said it planned to “expedite the development and review” of a drug for that use.

Colorado, as much as anywhere in America, knows its way around psychedelics. There are Psychedelic Professionals meetups and lots of ketamine clinics. "Secret" ayahuasca and peyote circles are not super-secret, and psychedelic therapists work underground, but not by much.

No large organizations endorsed shroom decriminalization — unless you think the Libertarians or the Greens qualify. But no group vocally opposed it, either. In the official voter information guide, the section for “arguments against the initiative” was blank.

After the initiative passed, Denver Mayor Michael Hancock, who had opposed it, said he would respect the will of the people. Jamie Giellis, his challenger in a June runoff election, was also against decriminalization and will honor the vote.

So expect a bumper crop of Denver shrooms this year, like a forest after a rainstorm — the law protects propagation. The growing materials, including mason jars, cost about $100 and can be found in any big-box store. The seeds of magic mushrooms, called spores, are not illegal, and can be ordered online.

A 10-week growing period yields more mushrooms than any user would reasonably want to consume, and the excess can legally be given away.

The initiative also creates a review panel to study the impact of decriminalization. The panel includes shroom advocates,City Council members, Denver residents, an addiction counselor and police officers.

Decriminalize Denver is trying to get ahead of potential bad publicity by mounting a public-information campaign, a sort of Psilocybin 101 — how much to dose, how and when it's best to trip, warning against driving while tripping, and cautioning to keep shrooms away from children.

Advocates note that the main part of the psilocybin fungus grows underground, establishing a network called mycelium that develops until the conditions are right — and then their fruit, mushrooms, pop into the light. The movement in Denver has already inspired Decriminalize Canada and Decriminalize California (in Oakland, it’s Decriminalize Nature). One or more of these efforts could well end up on a ballot in 2020.

Read more:

Paul Waldman: How marijuana is going to become bipartisan

Cynthia H. Coffman: It is too late to dismantle the marijuana industry

The Post’s View: Bowser’s proposal to legalize the sale of marijuana will lead to a fight with Congress. Bring it on.

Karl A. Racine and David Grosso: Congress, stop blocking D.C. from regulating its marijuana market

The Post’s View: What needs to happen before we legalize marijuana