Cannabis has been described as one of the most commonly used illegal substances worldwide (United Nations Office on Drugs and Crime, 2026a). However, depending on where you live, it might not be illegal anymore! In the modern world, cannabis policy environments vary considerably between and within countries (United Nations Office on Drugs and Crime, 2026b). In some countries, commercialised cannabis policy has allowed an explosion of retailers and an ever-expanding range of high THC concentration products (Schauer, 2021). On the other hand, some countries have Government-led legalisation frameworks which limit cannabis product availability and their THC concentration (Queirolo et al., 2025), or cannabis use is still criminalised.
Given the recent liberalisation of cannabis policy, many people may well ask, “well what’s the harm?”. But it’s important not to conflate legal availability with a lack of risk.
Cannabis use has been associated with a wide range of mental health conditions and cannabis use disorder (Petrilli et al., 2022). What is less clear is the role of cannabis use in some mental health conditions, and whether cannabis use patterns change in environments with greater availability and higher THC concentration products. For instance, some people have a sneaky puff on a joint at a party every so often. But some people 420 blaze it on a high-THC vape pen that they can buy from their local dispensary! These distinctions in THC concentration and frequency of use are important, as is the cannabis environment that facilitates their use.
Thankfully, two recent reviews in The Lancet Psychiatry (i.e., a prestigious academic journal) aimed to answer these questions. Hall et al. (2026) examined the association between regular cannabis use and the occurrence of mental health conditions. Freeman et al. (2026) examined changes in cannabis policy environments and their association with cannabis use, mental health conditions and cannabis use disorder.
Methods
Hall et al. (2026) systematically reviewed the existing evidence on the association between cannabis use and anxiety, depression, bipolar disorder, psychosis, and suicidal behaviour. The authors used a two-step process that first searched for evidence within high-quality systematic reviews and meta-analyses, then additionally included original research papers not captured in earlier reviews. In this important review, the authors triangulated evidence from prospective epidemiological studies alongside genetically informed, clinical, experimental and preclinical evidence. Their aim was to understand whether findings from studies with different data sources pointed towards similar conclusions about mental health conditions and cannabis use.
Freeman et al. (2026) reviewed the existing evidence on key changes in international cannabis policies over a staggering 25-year period (from 2000 to 2025) and their association with cannabis use and mental health conditions. They searched several academic databases for relevant studies, while information on international cannabis policies was informed by authors with expertise in their respective world regions and other relevant regional sources.
Results
Freeman et al. (2026) concluded that commercialised legal markets for recreational cannabis in Canada and the USA were associated with increased cannabis use and cannabis use disorder among adults. They also found an increase in THC concentration of cannabis products following commercialised legalisation in these countries (Freeman et al., 2026).
Some commercialised cannabis environments were associated with increases in hospital visits for psychosis and for psychotic conditions occurring alongside cannabis use disorder. However, there was no consistent evidence that policy change was associated with the prevalence or incidence of psychotic disorders. The authors reported that these associations were often stronger in places with more cannabis retailers and greater availability of high THC concentration cannabis products.
Ontario, Canada, provided an interesting case study within the paper. Cannabis-related health-care presentations had already started to increase before legalisation, making it difficult to attribute entirely to the policy change. However, cannabis-related anxiety emergency department visits increased by 31.4% between 2020 and 2022, in parallel to a known increase in the number of cannabis retailers and diversification of the available cannabis products at that time.
The contrast with more tightly controlled markets is instructive. The authors described Uruguay, which legalised recreational cannabis nationally but adopted a tightly controlled, state-regulated model. Cannabis can be accessed through a comparatively limited number of pharmacies, home cultivation and not-for-profit cannabis clubs, with the government controlling the price, products and THC concentration of cannabis sold. The limited evidence reviewed did not suggest increases in cannabis use among youth and young adults, although only two studies were available and follow-up was relatively short.
In a timely complement to Freeman et al. (2026)’s review, Hall et al. (2026) triangulated genetic, epidemiological and experimental evidence to conclude that daily cannabis use is a contributory cause of psychosis, acting alongside other risk factors. The earlier people start using cannabis, the more often they use it, the higher the THC concentration of the product and the longer the period of daily use, the greater the risk appears to be.
The evidence linking regular cannabis use with anxiety, bipolar disorder, depression and suicidal behaviour was less certain than that for psychosis. These associations may partly reflect cannabis use contributing to poorer mental health, but alternative explanations include self-medication, shared risk factors and bidirectional relationships.
Conclusions
Freeman et al. (2026) suggest that different cannabis policies, particularly highly commercialised environments, may be associated with increased cannabis use and the THC concentration of cannabis used. Hall et al. (2026) suggest that frequent cannabis use and the use of high THC concentration products are associated with a greater risk of psychosis. Evidence for associations with other mental health conditions, including anxiety, depression, bipolar disorder and suicidal behaviour, remains less certain. Together, these reviews suggest that both patterns of cannabis use and the policy environments that shape the availability and potency of cannabis products may be important when considering the mental health risks of using cannabis.
Strengths and limitations
A major strength of Hall et al. (2026)’s approach is their triangulation of the available evidence. Establishing whether cannabis contributes causally to mental conditions is notoriously difficult. People may use cannabis because they are experiencing mental health symptoms; cannabis use and mental health conditions may share common causes; and cannabis may itself contribute to mental health symptoms. Looking for consistency across research designs with different strengths and weaknesses provides greater confidence than relying on a single type of study.
One limitation is that, although Hall et al. (2026) drew evidence from multiple study designs, the strength of the evidence is not reported in text using an approach such as GRADE. The authors prioritise recent systematic reviews and assess whether findings are coherent across methodologies, but it could be helpful for the reader to know more explicitly in text about the quality of the different forms of evidence. With that said, the review is the most comprehensive to date on the topic.
The international policy review by Freeman et al. (2026) moves beyond treating cannabis legalisation as a simple yes/no question. Comparing different regulatory approaches is important because cannabis environments can vary enormously in product availability, THC concentration, and number of retailers. However, cannabis use may already be changing before a law is introduced, and the assessment of public health outcomes relies on the data available, which is a limitation regarding the associations with mental health outcomes. For instance, adult cannabis legalisation in Ontario and BC was preceded by extremely liberal medical cannabis programs that sold high-THC cannabis extracts and vaporisers.
Given that Freeman et al. (2026) synthesise a broad range of studies, it may be helpful in future work to stratify the findings by the quality of the evidence for each outcome. This could assist in interpreting the literature, particularly where multiple studies from the same country examine similar outcomes, as is often the case in Canada and the United States. It may also be useful to consider whether study findings differ according to the presence or absence of conflicts of interest. Given the substantial commercial involvement in the cannabis field (Grundy et al., 2023), examining whether conflicts of interest are associated with the direction or magnitude of reported findings could provide additional context for interpreting the evidence.
Implications for practice
Given the changing availability and potency of cannabis, clinicians should prioritise screening whether a patient uses cannabis, how frequently they use it and the THC concentration of products used. It is important to track both cannabis use patterns and potential adverse effects over time. As a broad recommendation, Hall et al. (2026) advocate for the cessation of cannabis use for people with mental health conditions. If abstinence is not a goal endorsed by the patient, they recommend reducing how often they use cannabis and the THC concentration of the products that they use.
Hall et al. (2026) also recommend that, given the high level of comorbidity, screening for cannabis use disorder among people with mental health conditions would be wise within clinical settings. It is important to remember that CUD is prevalent even in people who use cannabis for medicinal reasons (Dawson et al., 2024), so this recommendation is prudent regardless of whether the cannabis environment allows recreational use. A suggestion for clinicians managing patients with medicinal cannabis authorisation would be to communicate with the patient’s healthcare team to ensure benefits and risks of medicinal cannabis are appropriately balanced, particularly if the patient is using high-THC medicinal products.
Moreover, Freeman et al. (2026) describe commercialisation in terms of expanding retail availability and higher-THC products. These features may increase sales and consumption, which is, after all, what commercial markets are designed to do. Within these environments, though, it may be even more important for clinicians to be monitoring the nuances of cannabis use among their patients.
Statement of interests
Danielle Dawson (DD) has worked with several of the researchers involved in these reviews on other research projects, but was not involved in the conceptualisation, analysis, or writing of either paper. DD’s own research examines cannabis use, cannabis-related harms, medicinal cannabis, and cannabis policy. DD has received research funding to undertake work related to cannabis and cannabis policy through the University of Queensland. These interests should be considered when interpreting DD’s commentary on the research. The views expressed in this commentary are DD’s own and do not reflect the views of her employer.
Editor
Edited by Dr Dafni Katsampa.
Links
Primary papers
Hall, Wayne; Yimer, Tesfa M.; Thorne, Rachel Lees; Hoch, Eva; Burke, Chloe; Gridley, Ad; Hurd, Yasmin L.; Wilson, Jack; Leung, Janni; Freeman, Tom P. (2026). Relationships between cannabis use and mental disorders: Assessing the coherence of evidence from studies with different methodologies. The Lancet Psychiatry, 13(7), 604–614.
Freeman, Tom P.; Thorne, Rachel Lees; Wadsworth, Elle; Carney, Tara; Castillo-Carniglia, Alvaro; Cerdá, Magdalena; Kalayasiri, Rasmon; Kilmer, Beau; Lorenzetti, Valentina; Manthey, Jakob; Myran, Daniel T.; Rivera-Aguirre, Ariadne; Rychert, Marta; Wilson, Jack; Yimer, Tesfa; Hall, Wayne. (2026). International cannabis policies and their association with cannabis use, cannabis use disorder, and other psychiatric disorders. The Lancet Psychiatry, 13(7), 615–626.
Other references
Dawson, D., Stjepanović, D., Lorenzetti, V., Cheung, C., Hall, W., & Leung, J. (2024). The prevalence of cannabis use disorders in people who use medicinal cannabis: A systematic review and meta-analysis. Drug and Alcohol Dependence, 257, 111263.
Grundy, Q., Imahori, D., Mahajan, S., Garner, G., Timothy, R., Sud, A., Soklaridis, S., & Buchman, D. Z. (2023). Cannabis companies and the sponsorship of scientific research: A cross-sectional Canadian case study. PLOS ONE, 18(1), e0280110.
Petrilli, K., Ofori, S., Hines, L., Taylor, G., Adams, S., & Freeman, T. P. (2022). Association of cannabis potency with mental ill health and addiction: A systematic review. The Lancet Psychiatry, 9(9), 736–750.
Queirolo, R., Repetto, L., Alonso, J., Álvarez, E., Sotto, B., Pardal, M., & Kilmer, B. (2025). Intended and unintended effects of cannabis regulation in Uruguay. Policy & Politics, 53(3), 553–570.
Schauer, G. L. (2021). Cannabis policy in the United States: Implications for public health. JNCI Monographs, 2021(58), 39–52.
United Nations Office on Drugs and Crime. (2026a). Cannabis legalization and regulations. World Drug Report 2026.
United Nations Office on Drugs and Crime. (2026b). Long-term trends in cannabis use. World Drug Report 2026.