A study of data from pre and post-cannabis legalisation in Canada has found no increase in admissions to hospitals for cannabis-related episodes of psychosis.
The relationship between cannabis use and episodes of psychosis is a contentious issue that is often raised by opponents of legalisation. Results from previous studies have been mixed, with some finding evidence to suggest cannabis use, particularly in adolescence, can be a cause of psychotic episodes, and others finding no association between the two.
The present study was published in The Canadian Journal of Psychiatry in February 2024 and used data collected from the three emergency departments (EDs) in Quebec City. The number of admissions for psychosis where evidence of cannabis use was present was compared by researchers to the number of admissions in the 12 months following legalisation.
Only admissions from adults aged 18 years and above were included in the data, and evidence of cannabis use was obtained from the patient’s medical records and included results of urine tests as well as clinical notes.
Scientists from the Department of Psychiatry and Neurosciences, Faculty of Medicine, Laval University, Québec, examined the data and found no significant differences between the number of admissions for cannabis-induced episodes of psychosis before and after the legalisation of adult-use cannabis use.
“The present study observed no increase in the proportion of ED consultations for a psychotic episode in which evidence for cannabis consumption was obtained before and after legalization, which is in line with previous studies stating that legalization had no significative impact on ED consultations for psychosis.” writes the study author.
The results of the present study are similar to those of a recent study also from Canada, in which hospital admissions for psychosis from 2104 to 2020 were closely examined for trends linked to legalisation in 2018. Despite identifying an increase in health service use and incident cases of substance-induced psychotic disorders they did not find a link to cannabis legalisation.
“We identified psychosis-related outpatient visits, emergency department visits, hospitalizations, and inpatient length of stay, as well as incident cases of psychotic disorders, among people aged 14 to 60 years.
We did not find evidence of increases in health service use or incident cases of psychotic disorders over the short-term (17-month) period following cannabis legalization. However, we found clear increasing trends in health service use and incident cases of substance-induced psychotic disorders over the entire observation window (2014–2020).” researchers from the earlier study wrote.
Researchers from the present study emphasised the limitations of the study and recommended further research to include a larger sample and a longer period of observation, warning against making strong conclusions based on the results due to several factors. “First, the information on cannabis use relied exclusively on information gathered in the medical records, which may lead to some misclassification as nonusers; however, as this limitation was present prior to and after legalization, it is an unlikely explanation for the lack of change in proportion. Second, while the present sample was sizeable, it might have lacked statistical power to detect a small impact of cannabis legalization, even more so in subsequent comparisons within patient subgroups, for example, FEP. Third, the one-year duration of the post-legalisation period examined did not allow for examination of the longer-term impact of legalization, being potentially affected by (1) increased awareness of psychosis in the media only after legalization; (2) inconsistent supply and variable opening hours of SQDC in the first months; (3) availability of very different Δ9-tetrahydrocannabinol (THC) concentrations.”
“In conclusion, considering these methodological issues, the present results do not suggest that cannabis legalization had a major impact on the number of ED consultations for psychotic disorders.”
