Christchurch, NZ: Those with a history of cannabis consumption do not exhibit more severe symptoms of psychosis than do those with no history of regular use, according to longitudinal data published in the New Zealand Medical Journal.
A team of New Zealand researchers assessed the relationship between marijuana use and the severity of psychotic symptomology in a cohort of over 1,200 subjects born in 1977. Investigators compared the symptom profile of cannabis consumers and non-consumers at age 18, 21, and at age 25.
Researchers reported that cannabis-consuming subjects were more likely than non-users to report experiencing a greater variety of psychotic symptoms overall. However, investigators acknowledged that consumers were not more likely to report experiencing severe symptoms.
Authors reported: “The present analyses sought to determine whether there was a qualitative difference in the kind of symptoms being reported by the two groups. … Both groups tended to report common, low-level symptoms (such as “having ideas or beliefs that others do not share”), and neither group was likely to report what would be considered as more severe positive symptoms of psychosis.”
They concluded: “Collectively, the results suggest that while those who were regular cannabis users reported a significantly greater number of symptoms than non-users, the symptom profile between the two groups did not differ, showing that there was no evidence of greater ‘severity’ among regular cannabis users.”
Although the use of cannabis and other controlled substances is more common among those with psychotic illnesses, studies indicate that lifetime incidences of marijuana-induced psychosis are relatively rare among those who do not already have a prior diagnosis of a psychiatric disease.
Full text of the study, “Cannabis use and patterns of psychotic symptomology in a longitudinal birth cohort,” appears in the New Zealand Medical Journal.