Cannabis use and patterns of psychotic symptomatology in a longitudinal birth cohort

AIM: Research has established associations between regular cannabis use and psychotic symptomatology in young people. However, there has been little previous research on whether the experience of psychotic symptomatology differs between non-users and regular users of cannabis. METHOD: Data were from the Christchurch Health and Development Study (CHDS), a longitudinal cohort born in 1977. Data on frequency of cannabis use and (past month) psychotic symptomatology were obtained at the age 18, 21 and 25 waves of assessment. Symptoms were rank ordered by the number of affirmative responses over the three assessments, and the symptom profile of non-users and regular users were compared using a non-parametric Mann-Whitney U test. RESULTS: Among non-users and regular users, the commonly reported symptoms of psychosis were those that would be considered "mild". More severe symptoms were not commonly reported. A comparison of the symptom profile across the two groups showed no significant differences. CONCLUSION: There was no evidence of qualitative differences in the pattern of psychotic symptomatology reported by non-cannabis users and regular cannabis users. Although regular cannabis users tend to report a greater number of symptoms, these symptoms did not tend to be severe, and were unlikely to be indicative of psychotic illness.