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Denver 2019: First US City to Decriminalize Psilocybin · Microdosing College
History
Denver 2019: The First US City to Decriminalize Psilocybin
By Microdosing College Editorial·Last updated June 14, 2026·7 min read
Denver and the Vote That Started a Wave
When Denver voters approved Ordinance 301 on 7 May 2019, they made their city the first in the United States to decriminalize psilocybin mushrooms — and they did it by the narrowest of margins. The final tally was roughly 50.6% in favour, 49.4% against, a gap of fewer than 2,000 votes out of more than 170,000 cast (Denverite, 2019). The closeness of the result underscored how contested the question was, and how much the outcome depended on months of street-level organizing by a small campaign called Decriminalize Denver.
Understanding what Ordinance 301 actually did — and did not do — is essential before drawing any broader conclusions. This is an article about policy history, not legal advice. Laws vary by jurisdiction, change over time, and the situation described here applies only to Denver, Colorado, in a specific historical moment.
The ordinance had a carefully limited scope. It did not legalise psilocybin under state or federal law; both Colorado state law and the federal Controlled Substances Act continued to classify psilocybin as a Schedule I substance. What Ordinance 301 did was instruct Denver city government and law enforcement to:
Make personal possession and use of psilocybin mushrooms by adults aged 21 and over the lowest law-enforcement priority.
Prohibit the use of city or county funds to impose criminal penalties on individuals for those offences.
Establish a Psilocybin Mushroom Policy Review Panel to monitor outcomes and report to the City Council.
Sale, distribution, and importation were explicitly outside the measure's scope. Cultivation in quantities consistent with personal use was arguably covered under possession, but the ordinance created no commercial pathway. It was a decriminalization measure in the strict sense: the act remained technically illegal under other legal codes, but the city would not spend resources prosecuting it.
This is a pattern that appears repeatedly in drug-policy reform — a city or county carving out a de-prosecution zone within a broader prohibitionist framework. It is less sweeping than it may sound, and it created real legal ambiguity for anyone caught in situations involving state troopers or federal agents, who were under no obligation to follow the city ordinance.
The Campaign Behind the Ballot
Decriminalize Denver was the grassroots organisation responsible for gathering the roughly 4,700 valid signatures needed to place the initiative on the May 2019 municipal ballot. The campaign drew heavily on two overlapping arguments: harm reduction (the evidence that psilocybin mushrooms have a low potential for physical dependence and do not contribute to public-safety crises) and therapeutic promise (the wave of clinical research then emerging from institutions like Johns Hopkins and NYU).
The Johns Hopkins connection was significant. In 2006, Roland Griffiths and colleagues had published a landmark study demonstrating that psilocybin could occasion mystical-type experiences of lasting personal meaning in healthy volunteers under controlled conditions (Griffiths et al., 2006, Psychopharmacology). That research, and the clinical work it catalysed, gave campaign organisers a credible scientific frame: they were not talking about recreational drug use but about a substance with demonstrated therapeutic signals and an unusually favourable safety profile in controlled settings.
Opponents — including Denver's mayor and city council, who formally opposed the measure — argued that the science was not yet settled enough to warrant even symbolic decriminalization, and that the initiative would send confusing messages to young people. The narrow margin suggests that both arguments resonated.
The Immediate Aftermath
The Psilocybin Mushroom Policy Review Panel met several times in 2019 and 2020 and produced reports finding no evidence of increased youth use or public-safety problems attributable to the ordinance. Arrests and prosecutions for psilocybin possession in Denver — which had already been rare — did not increase, and there was no measurable surge in emergency-room visits linked to mushroom use in the city.
These findings, while limited in scope, were widely cited by decriminalization advocates in other cities. Within eighteen months, Oakland and Santa Cruz in California had passed their own decriminalization measures. The organisation Decriminalize Nature, founded partly on the Denver model, helped spread similar resolutions to Ann Arbor, Washington DC, Somerville, Cambridge, Northampton, and beyond.
Colorado itself went further in November 2022, when voters approved Proposition 122 (the Natural Medicine Health Act), which created a regulated framework for therapeutic psilocybin access — a considerably more expansive step that built, in part, on the cultural and political ground broken by Ordinance 301. Denver's 2019 vote was, in retrospect, the first public test of whether a US electorate would back psilocybin reform at the ballot box. The answer was yes, but only just.
Where Denver Fits in the Longer History
The 2019 vote did not emerge from nowhere. It came at the tail end of a decades-long arc that began with the criminalisation of psilocybin under the Controlled Substances Act of 1970 and the subsequent scheduling that took full effect in 1971 — a policy moment explored in our psilocybin scheduling 1971 backlash article. That scheduling froze clinical research for roughly two decades and drove any exploration of psilocybin's effects underground.
The renaissance that eventually made Denver possible was itself a decades-long project. Griffiths' 2006 Johns Hopkins study was a pivotal turning point, but it built on earlier neuropsychopharmacology research and on the surviving ethnobotanical and clinical records from the 1950s and 1960s. By 2019, a critical mass of peer-reviewed literature, a generation of researchers trained specifically in psychedelic science, and a set of positive phase-2 clinical trials for depression and end-of-life anxiety had shifted the conversation enough that a ballot initiative in a mid-sized American city could succeed.
None of that history negates the need for caution. Decriminalization is not a safety certification. Psilocybin mushrooms carry genuine risks — psychological distress, dangerous interactions with certain medications, and particular concerns for people with personal or family histories of psychosis. Nothing in Ordinance 301 or the research record justifies describing psilocybin as simply "safe," and no policy change replaces individual screening and informed decision-making. If you are considering psilocybin for personal or therapeutic reasons, our screener is a starting point, and our research library gathers the primary literature without editorialising beyond what the data support.
What Came Next and What Still Varies
As of mid-2026, the landscape in the United States is deeply uneven. Oregon's Measure 109, passed in 2020, created the first state-level licensed therapeutic psilocybin programme. Colorado's Proposition 122 is in implementation. Dozens of cities have decriminalization resolutions. But at the federal level, psilocybin remains a Schedule I controlled substance, and in most US states personal possession is still a criminal offence.
Denver's Ordinance 301 is best understood as a historical hinge point: the moment the modern US decriminalization movement proved it could win a public vote. It opened a door. What lies beyond that door — regulated therapy, cautious harm reduction, or something else — is still being negotiated city by city, state by state, and in the research literature.
For deeper context on how these debates connect to the full sweep of psychedelic history, see the history of psychedelic mushrooms pillar hub.
Frequently asked
What did Denver's Ordinance 301 actually do?+
Passed on 7 May 2019, Ordinance 301 made personal possession and use of psilocybin mushrooms by adults the lowest law-enforcement priority in Denver and prohibited city funds from being used to prosecute those offences. It did not legalise psilocybin under state or federal law.
By how much did Denver's psilocybin decriminalization measure pass?+
The margin was extremely narrow — approximately 50.6% in favour versus 49.4% against, a difference of fewer than 2,000 votes out of roughly 170,000 cast, according to contemporaneous reporting by Denverite.
Did decriminalization in Denver make psilocybin legal?+
No. Psilocybin remained a Schedule I controlled substance under Colorado state law and the federal Controlled Substances Act. The ordinance only directed city authorities not to prioritise enforcement; state and federal law enforcement were unaffected.
What happened after Denver's vote — did other cities follow?+
Yes. Oakland and Santa Cruz followed within eighteen months. A wave of similar resolutions passed in cities including Ann Arbor, Washington DC, and Somerville. Colorado went further in 2022 with Proposition 122, which created a regulated therapeutic psilocybin framework.
Is psilocybin decriminalized where I live?+
Laws vary significantly by city, state, and country. Denver's ordinance applies only within Denver city limits. Check current local law rather than assuming decriminalization applies in your area; this article is historical education, not legal advice.
This guide is general educational information about microdosing, not medical advice and not a recommendation to use any substance. It can't account for your personal health. If you take medication or live with a mental-health condition, speak with a qualified professional before making any decision.
