A new study has found no significant increase in the rates of psychosis-related diagnoses in states which have introduced cannabis policies.
Researchers from the Hospital of the University of Pennsylvania in Philadelphia found no ‘statistically significant difference’ in the rates of psychosis-related diagnoses, or prescribed antipsychotics, in states with medical or recreational cannabis policies compared to those where the plant is still prohibited.
For the study scientists examined commercial and Medicare Advantage claims data from more than 63 million individuals between 2003 to 2017.
The number of unique claims with psychosis-related diagnoses, prescribed antipsychotics and follow-up time was analysed, alongside measures of state cannabis policy and state-level demographic, social, and economic characteristics.
A total of 29 US states adopted cannabis policies during the time period. The analysis focused on legalisation policies in which personal use, cultivation, production, promotion and sale is permitted.
Results from multiple analyses showed no ‘statistically significant increase’ in rates of psychosis-related diagnoses or prescribed antipsychotics in states with either medical or adult-use retail outlets, compared to those with no cannabis policy in place.
However, in secondary analyses, rates of psychosis-related diagnoses were found to increase among men, people aged 55 to 64 years and those of Asian heritage, in states with recreational policies compared with no policy.
It is also important to note that due to the design of the study it was only able to capture data from those who received treatment for their diagnosis.
The authors state: “As states continue to introduce cannabis policies, the implications of state cannabis legalisation for psychotic disorders warrants continued study, particularly in data settings where direct measures of disease onset and severity are available.”
Cannabis and psychosis in context
Psychosis is described by the NHS as someone ‘losing touch with reality’. Its two main symptoms come in the form of hallucinations – seeing or hearing things that other people cannot – and delusions, when a person believes things that are not actually true.
It is widely regarded by critics of cannabis to be a consequence of consumption and is often used as an argument against policy reform. But claims that have been cited in the media for decades that ‘all cannabis causes psychosis’ are unfounded.
While some studies have reported associations between cannabis use and psychosis, whether it plays a causal role in the onset of psychotic symptoms remains unclear. A number of factors such as THC potency, frequency of use, and the age and genetics of the consumer may all contribute to the risk of developing psychosis.
According to the authors of this latest paper, a small number of previous studies have reported increased rates of psychosis in association with local cannabis policies, although most have focused on either medical or recreational policies in isolation.
They have advised that further studies are carried out, as an increasing number of jurisdictions across the world make moves to introduce more liberal cannabis laws.
The paper concludes: “In this retrospective cohort study of commercial and Medicare Advantage claims data, state medical and recreational cannabis policies were not associated with a statistically significant increase in rates of psychosis-related health outcomes.
“As states continue to introduce new cannabis policies, continued evaluation of psychosis as a potential consequence of state cannabis legalisation may be informative.”
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