No Link Between Legal Cannabis and Psychosis Diagnoses, Study Finds
Legalizing cannabis does not affect psychosis diagnoses or the prescription of antipsychotic medicines, a new study published in JAMA Network Open has found.
Psychosis has long been associated with cannabis use, with numerous longitudinal studies suggesting links between long-term cannabis use and the onset of schizophrenia and other psychotic disorders.
However, this latest study of data from more than 63 million people found no statistically significant changes in psychosis-related diagnoses or prescribed antipsychotics after states implemented legal medical or recreational cannabis laws.
As states continue to pursue cannabis legalization measures, monitoring psychosis-related health outcomes and healthcare utilization will become an important area for continued study, the researchers say.
Legalization does not affect psychosis
For this latest study, researchers used the Optum Clinformatics Data Mart Database, which contains deidentified information relating to commercial and Medicare Advantages claims from more than 63 million people, recorded between 2003 and 2017.
They searched the database for claims containing psychosis-related diagnosis codes and/or antipsychotics prescriptions. This data were then combined with data on the cannabis policies of each state during the study time period. In addition to recording whether a state had no legal cannabis policy, a medical-only policy, or a recreational cannabis policy, the researchers also recorded whether a state had active retail outlets. State-level demographic, social, and economic characteristics were also considered.
The researchers found no statistically significant increases in the rates of psychosis-related diagnoses in states with legal medical or recreational cannabis, versus states where cannabis remained prohibited. They also found no significant changes in claims made for antipsychotics prescriptions.
To examine whether there might be any differences among different demographic populations, the researchers also carried out a series of exploratory secondary analyses. Unlike the primary analyses, these secondary analyses were not adjusted for multiple comparisons. Still, they once again found no increases in prescribed antipsychotics after legalization.
However, in the secondary analyses the rates of psychosis-related diagnoses did increase in states with recreational cannabis policies among men, those aged 55 to 64, and Asian claimants, compared to states that maintained prohibition. While the overall rates of diagnoses did not change, the researchers say that this demographic finding should “underscore the importance of continued examination of heterogeneous effects of cannabis policies” and encourage further research on cannabis and health inequities.
More research needed to reflect vulnerable groups
This is the largest study to date examining the relationship between medical and recreational cannabis policies and rates of psychosis-related healthcare claims. For this reason, the study’s finding, that legalization had no significant overall impact on psychosis-related diagnoses or prescriptions, is a significant one.
However, the researchers do note a number of limitations of this study, which could become areas for future research. For example, because the study was designed to examine healthcare claims that were made, this dataset only reflects those cases where an individual was able to access healthcare services and successfully receive a diagnosis or treatment. As a result, it is possible that some vulnerable groups might not have been reflected in this analysis.
The researchers also note that the dataset did not distinguish new psychotic disorders from pre-existing ones, so it is possible that state legalization could be affecting incident vs prevalent psychosis differently.
“As psychotic disorders are associated with lower socioeconomic position, generalizability of our study findings is limited by our focus on insured individuals likely with fluctuating representativeness within states over the study period.” the researchers wrote.
“As states continue to introduce cannabis policies, the implications of state cannabis legalization for psychotic disorders warrants continued study, particularly in data settings where direct measures of disease onset and severity are available.”
Cannabis and psychosis
While more research is needed to definitively determine whether there is a correlation between cannabis legalization and psychosis, there are numerous studies that have tied the use of high-potency cannabis products to an increased risk of experiencing psychotic episodes.
In a 2022 systematic review published in the Lancet Psychiatry, researchers from the Addiction and Mental Health Group at the University of Bath, England, found that high-potency cannabis products were associated with an increased risk of developing psychosis, as well as an earlier age of onset for psychotic disorders compared to low-potency cannabis users.
Another study from scientists at the University of Cologne, published in Scientific Reports, found that frequent cannabis use was also associated with an increased risk of experiencing specific psychotic symptoms, such as persecutory delusions or believing that others can hear your own thoughts. They also found that the younger a person was when they first initiated cannabis use, the more likely they were to experience visual hallucinations.
In contrast, other research studies have suggested that CBD may have an antipsychotic effect in individuals with psychosis. Published in Psychological Medicine, one study has even suggested a potential mechanism that could explain the cannabinoid’s antipsychotic effects. The study found that a single dose of CBD partially boosted activity in two brain regions associated with decision-making and conscious memory. Over- and under-activation in these regions has previously been reported in individuals with schizophrenia; the researchers said this may be an avenue for further research.