Summary: Decriminalizing personal cannabis possession or implementing tightly controlled legal frameworks does not appear to increase overall use. In contrast, fully commercialized, for-profit recreational markets — like those in parts of the United States and Canada — are linked to higher product potency, rising addiction rates, and increased hospital admissions for psychosis. A separate review of 54 clinical trials found limited evidence supporting medical cannabinoids for primary psychiatric conditions such as anxiety, PTSD, or depression, with only modest benefits observed for insomnia, some autism traits, and cannabis withdrawal.
Key Facts
- Policy design matters: Decriminalization or strict state-controlled access (capping potency and limiting market scale) shows little evidence of increasing population-level cannabis consumption.
- Commercialization increases harm: Large-scale, for-profit markets in the US and Canada are associated with increased availability, higher THC potency, and rising cannabis use disorder among adults.
- Psychiatric admissions rise in commercial markets: Commercialized legal systems are correlated with more hospital admissions for psychosis, particularly where psychotic disorders co-occur with cannabis use disorder.
- Justice and equity impacts: Shifting from criminal penalties to health-focused models through decriminalization can reduce racially disproportionate policing and redirect responses toward healthcare.
- Limited clinical support for psychiatric uses: Across 54 trials, cannabinoids showed modest effects for insomnia, some autism-related traits, and reducing cannabis withdrawal, but no meaningful benefit for anxiety, PTSD, psychosis, or opioid dependence; no trials evaluated depression treatment.
Source: University of Bath
Global policy trends and public health outcomes
A multidisciplinary team led by researchers at the University of Bath analyzed international cannabis policy changes between 2000 and 2025 and their relationships with cannabis use, cannabis use disorder, and other psychiatric outcomes. Their analysis, published in The Lancet Psychiatry, distinguishes outcomes from different regulatory approaches — from prohibition and decriminalization to tightly regulated supply and fully commercialized legalization.
The study finds that decriminalizing possession for personal use or adopting tightly regulated legal access (for example, capped product potency and limited retail availability) generally did not produce increases in population-level cannabis use. Uruguay is highlighted as an example of a tightly controlled legalization model where adults can obtain limited-potency products through pharmacies, join regulated social clubs, or grow for personal use, without strong evidence of increased consumption.
By contrast, in jurisdictions where recreational cannabis is sold through well-developed for-profit retail systems — notably parts of Canada and many US states — the research links commercialization to greater product availability and escalating THC potency. These markets have seen increases in adult prevalence of use and in cannabis use disorder, characterized by difficulty stopping use despite negative life impacts. The authors note that in the US there are now more daily cannabis consumers than daily alcohol consumers, a market shift that coincided with rising addiction and more hospital admissions for psychosis, including cases where psychosis and cannabis use disorder occur together.
Lead authors emphasize that how a policy is changed matters more than whether change occurs. Alternative strategies such as decriminalization or strictly regulated legalization can remove criminal penalties and reduce harms associated with enforcement while limiting expansions in consumption and commercial influence.
Medical cannabis and clinical evidence
The review also examined medical cannabis policy and the clinical evidence for cannabinoids in treating psychiatric disorders. The researchers warn that poorly regulated medical access, especially when efficacy and safety data are limited, may increase health risks. A systematic synthesis of 54 clinical trials showed only modest therapeutic effects: improvements in sleep for insomnia, slight reductions in cannabis withdrawal and use, and benefits for certain tics and autism traits. Conversely, cannabinoids were associated with increased cocaine craving among people with cocaine use disorder and produced no meaningful benefit for anxiety, PTSD, psychosis, or opioid dependence. No completed trials addressed depression treatment.
The findings underline the need for cautious, evidence-driven medical cannabis policies and improved monitoring where medical access is expanded.
Frequently asked questions
A: No. Analysis of data from 2000–2025 indicates that removing criminal penalties for personal possession generally does not increase population-level consumption. Decriminalization tends to reframe responses from punishment to healthcare without broadening the user base.
A: The research attributes much of the difference to commercialization. For-profit markets promote product availability, active marketing, and escalating THC potency — factors that can increase addiction risk and emergency admissions for psychosis.
A: A systematic review of 54 trials found little robust evidence supporting cannabinoids for anxiety, PTSD, or opioid dependence, and no completed trials for depression. Limited benefits appeared for sleep, cannabis withdrawal, and certain autism-related traits.
Editorial notes
- This article was edited by a Neuroscience News editor.
- The underlying journal paper was reviewed in full by the editorial team.
- Additional context was added by staff to clarify policy and clinical implications.
About this research
Author: Vittoria D’Alessio
Source: University of Bath
Contact: Vittoria D’Alessio, University of Bath
Image: Image credited to Neuroscience News
Original research: Freeman TP, Lees Thorne R, Wadsworth E, Carney T, Castillo-Carniglia A, Cerdá M, Kalayasiri Q, Kilmer B, Lorenzetti V, Manthey J, Myran DT, Rivera-Aguirre A, Rychert M, Wilson J, Yimer T, Hall W. International cannabis policies and their association with cannabis use, cannabis use disorder, and other psychiatric disorders. Lancet Psychiatry. DOI: 10.1016/S2215-0366(26)00087-8 (open access).
Abstract
Cannabis policies range from prohibition to commercialized legalization and have changed rapidly across jurisdictions. This review assessed evidence linking international policy shifts from 2000–2025 to cannabis use, cannabis use disorder, and psychiatric outcomes. Commercialized non-medical markets in Canada and the USA were associated with higher adult prevalence of cannabis use and cannabis use disorder and with increases in cannabis potency since legalization. There was no consistent evidence that policy change altered the prevalence or incidence of psychotic disorders overall, but commercialized legalization was associated with increased hospital admissions for psychosis and for psychotic disorders comorbid with cannabis use disorder. Poorly regulated legal medical access, absent clear efficacy and safety data, could raise risk of harm. Policies that limit commercialization appeared less strongly associated with increased use or psychiatric disorders, though long-term monitoring is needed. Decriminalization in Europe, Africa, Oceania, and Asia showed little evidence of changing use or psychiatric disorder rates.