Study fails to identify cannabis exposure as risk factor for development of psychosis
According to data published in the journal Psychiatry and Clinical Neurosciences, a history of cannabis use is not associated with an increased risk of developing psychosis, even in people predisposed to this disorder.
Case-control studies suggest that cannabis use is a risk factor for the development of psychosis. However, prospective studies are limited and the direction of this association remains controversial.
A team of Australian, European and British researchers examined the association between cannabis use and the incidence of psychotic disorders in clinically at-risk subjects. The researchers assessed the subjects at baseline and followed them for two years.
The main objective of the present study was to examine the association between cannabis use and the incidence of psychotic disorders in people at high clinical risk for psychosis. Secondary objectives were to assess associations between cannabis use and persistence of psychotic symptoms, as well as functional outcomes.
They reported the following: “There was no significant association between a measure of cannabis use at baseline and transition to psychosis, symptom persistence, or functional outcomes.
The authors conclude: “Our primary hypothesis was that cannabis use in CHR [clinically high-risk] subjects would be associated with an increased rate of subsequent progression to psychosis. However, there was no significant association with any measure of cannabis use. … These results are inconsistent with epidemiological data linking cannabis use to an increased risk of developing psychosis.”
During follow-up, 16,2% of the high-risk clinical sample developed psychosis. Of those who did not become psychotic, 51,4% had persistent symptoms and 48,6% were in remission. There was no significant association between any measure of cannabis use at baseline and transition to psychosis, persistence of symptoms, or functional outcomes
These results contrast with epidemiological data which suggests that cannabis use increases the risk of psychotic disorders. Although the use of cannabis and other controlled substances tends to be more common among people with psychotic illnesses, studies indicate that the lifetime incidences of marijuana-induced acute psychosis are relatively rare in the general population.
Data published last year in the New Zealand Medical Journal indicates that people with a history of cannabis use generally do not have more severe symptoms of psychosis than people without a history of regular use.
