Allowing the commercialisation of cannabis could contribute to problematic use

Embargoed until: Publicly released: 2026-06-18 08:30

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Countries that have legalised cannabis and allowed the commercialisation of the drug have seen higher usage and a subsequent increase in cannabis use disorder, according to a review by Australian and international researchers. The team looked at changes to cannabis policy around the world since 2000, and they say while decriminalising the drug did not appear to be linked to any increase in cannabis use or psychiatric disorders, in Canada and the USA where commercial supply is legal, there was been an increase in use, problematic use and an increase in psychosis-related hospital visits for people with cannabis use disorder. In a second review, international and Australian researchers analyse the evidence around how cannabis impacts mental health. They say the evidence shows a consistent link between regular cannabis use and a higher risk of psychosis. Evidence is less clear around anxiety, depression and specific psychotic disorders, they say, as links between the two could simply mean people are self-medicating using the drug or that people with mental health struggles are more likely to use it more often.

News release

From: The Lancet

The Lancet Psychiatry: Cannabis legalisation associated with increase in cannabis use disorder and cannabis potency, review highlights

Data from Canada and the USA suggest non-medical cannabis legalisation is associated with increased rates of cannabis use and cannabis use disorder in adults, as well as an increase in cannabis potency, highlights a global review published in The Lancet Psychiatry journal. Additionally, legalisation in Canada and the USA was associated with an increase in hospital visits related to psychosis and psychotic disorders in patients who also had cannabis use disorder, however there was not consistent evidence for a link between cannabis legalisation and rates of psychotic disorders.

Non-medical cannabis use by adults is banned in many countries but has been decriminalised in large parts of the Americas, Europe, and Australia. As cannabis can be addictive and is also linked to an increased risk of psychosis, it is important that the potential impact of cannabis policy changes on cannabis use and associated medical conditions is monitored.

The review looked at research on trends associated with changes to cannabis policies from 2000 to 2025. The authors found the link in the USA and Canada between cannabis legalisation and an increase in cannabis use disorder was stronger when there was an expansion of retail stores and sale of higher potency cannabis products, suggesting greater commercialisation may increase the risk of problematic use.

Compared to some US states that have few restrictions on cannabis products, in countries that heavily regulate via the market with limits on potency, price, and availability, there is little evidence for an association between policy change and cannabis use and addiction.

The review found scarce evidence of associations between changes in cannabis policies and cannabis use, cannabis use disorder, or other psychiatric disorders in Europe, Africa and Oceania, consistent with the limited scale of policy change or commercialisation in these regions when compared to the USA or Canada.

The authors say cannabis legalisation, especially when heavily commercialised with limited regulation, may increase the risk of harms from cannabis use. They call for more research to better monitor the potential impacts of legalisation.

A second review on cannabis published in the same issue of The Lancet Psychiatry journal finds evidence that daily cannabis use acts with other risk factors to increase the risk of psychosis, but its role in depression, anxiety and risk of suicidal thoughts or suicide was less clear.

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Journal/
conference: The Lancet Psychiatry

Research:Paper

Organisation/s: Australian Catholic University, The University of Queensland, The University of Sydney, University of Bath, UK

Funder: Paper 1 - TPF was funded by a UKRI Future Leaders Fellowship (number: MR/Y017560/1). None of the funding sources had any role in the writing of the manuscript or the decision to submit it for publication. Paper 2 - TPF was funded by a UKRI Future Leaders Fellowship (MR/Y017560/1). JL was funded by an Australian National health and Medical Research Council Investigator grant. None of the funding sources had any role in the writing of the manuscript or the decision to submit it for publication.

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