Oregon Psilocybin Decriminalization: New JAMA Study Reveals 90,000 Extra Users

Published March 18, 2026 · 6 min read

Oregon psilocybin decriminalization: what changed and when

In November 2020, Oregon voters passed Measure 110. This law decriminalized personal possession of all controlled substances, including psilocybin mushrooms. Consequently, Oregon became the first US state to treat drug possession as a public health issue rather than a criminal one. Two years later, in 2022, Colorado followed with its Natural Medicine Act. That law decriminalized psilocybin and other natural psychedelics for personal use. In addition, it established a framework for supervised therapeutic access.

For years, researchers suspected these policy changes were fuelling increased use. However, separating the policy effect from broader cultural shifts was difficult. These shifts include the so-called psychedelic renaissance, growing media attention, and expanding mental health discourse. That is exactly the gap this JAMA study set out to fill.

Wild Psilocybe semilanceata mushrooms in nature

The JAMA study: methodology and key findings on psilocybin decriminalization

The study was led by Joshua C. Black, PhD, and colleagues at Rocky Mountain Poison & Drug Safety in Denver. Specifically, it drew on 15 waves of the national Survey of Non-Medical Use of Prescription Drugs. In total, the survey collected responses from 441,734 people between 2018 and 2025. Participants reported whether they had used psilocybin in the past 12 months.

Rather than simply observing trends, the team used an augmented synthetic control method. In essence, this is a causal inference technique that builds a statistical "what-if" scenario. It uses data from all 48 other states and Washington D.C. as a comparison. Moreover, the model controlled for demographic, socioeconomic, and health-related factors. As a result, it could estimate what psilocybin use in Oregon and Colorado would have looked like if the law had never changed.

Notably, the most striking finding concerns Oregon's licensed psilocybin programme. The estimated increase caused by Oregon psilocybin decriminalization exceeded the number of people visiting official service centres. Oregon now has nearly 30 licensed facilities, but sessions cost between $1,000 and $3,000. Therefore, the data strongly suggests that most new use happened outside clinical settings. Put simply: when you decriminalize, most new users do not go to a clinic.

What does this mean for drug policy?

Lead researcher Dr. Joshua Black summarised the significance concisely: "This study answers the question policymakers actually face. How many additional people used a substance because the law changed?" Indeed, answering that question requires causal inference methodology — not just trend reporting. This makes the Oregon psilocybin decriminalization study unique in the field.

Furthermore, the findings land at a pivotal moment. Oregon has already partially rolled back Measure 110 through House Bill 4002, signed in 2024. That bill recriminalized personal possession of most controlled substances, including psilocybin. This happened in response to the opioid crisis. However, researchers found no causal link between Measure 110 and overdose deaths. Meanwhile, supervised psilocybin therapy under Measure 109 remains legal. Still, personal non-clinical use is once again a criminal misdemeanour in the state.

Colorado's approach, on the other hand, combines personal-use decriminalization with a licensed supervised-use framework. This includes home cultivation and sharing. As a result, it may become a template for other states. The JAMA study could not yet draw firm conclusions for Colorado because the post-policy window was too short. Even so, the directional data points to a similar pattern.

Oregon psilocybin decriminalization in the global context

Importantly, the United States is not acting in isolation. Globally, psilocybin policy is shifting faster than at any point in modern history. For instance, Australia became the first country to approve psilocybin as a prescription medicine in 2023. Similarly, the Czech Republic became the first EU country to allow medical psilocybin therapy in early 2026. In addition, the EU-funded PsyPal trial led by University Medical Centre Groningen is running large-scale clinical trials across Europe.

Above all, the JAMA findings add a crucial dimension to this global conversation. Policy changes do not just affect who can access psilocybin therapeutically. In fact, they reshape use patterns across the whole population. As the authors note, regulators everywhere will need to weigh the potential benefits alongside the risks of both regulated and unregulated use.

Dense cluster of Psilocybe cubensis in a grow tray

For readers in North America

For readers in Europe: explore our full range

If you are based in Europe, you are in luck. Indeed, the Netherlands is home to one of the most progressive frameworks for psilocybin products. Moreover, the Magic Mushrooms Shop has been serving the European community for many years. While the Oregon psilocybin decriminalization debate plays out in the US, Europeans already have access. Here is what we offer:

Frequently asked questions about the JAMA psilocybin decriminalization study

What exactly did Oregon decriminalize?

Oregon's Measure 110 (2020) decriminalized personal possession of all controlled substances, including psilocybin. In addition, a separate measure — Measure 109 — legalized supervised therapeutic use at licensed service centres. However, in 2024 personal possession was recriminalized via House Bill 4002. Supervised therapeutic use under Measure 109 still remains legal.

Does the study prove that decriminalization causes harm?

No. The Oregon psilocybin decriminalization study only measures the increase in use. It does not measure outcomes. Moreover, the researchers explicitly call for balanced policy decisions. Critically, no causal link between Measure 110 and Oregon's opioid crisis was found. Instead, overdose increases were attributed to fentanyl spreading through the drug supply.

Why were the results for Colorado less clear?

Colorado's Natural Medicine Act was passed in 2022, two years after Oregon's Measure 110. As a result, the JAMA study had only a short post-policy window for Colorado. The direction of the effect was similar (+1.8 percentage points). However, the data were insufficient to reach statistical significance. Therefore, a longer follow-up study is needed.

What does "synthetic control method" mean?

In short, it is a statistical technique from the causal inference field. It creates a "composite control state" from weighted combinations of other states' data. Consequently, researchers can estimate what Oregon would have looked like without decriminalization. This isolates the policy effect from broader trends in psychedelic use.

Source: Black JC et al. Psilocybin Trends in States That Decriminalized Use. JAMA. 2026. DOI: 10.1001/jama.2026.1952. Published March 10, 2026.