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Cannabis use may prompt transition to psychosis

10 May 2007

Cannabis use is strongly associated with the development of psychosis among people at risk of the disorder, research indicates.

The finding supports the notion that cannabis use is a risk factor for schizophrenia and strengthens the case for screening and monitoring at-risk individuals for cannabis use.

Study authors Karin Kristensen and Kristen Cadenhead (University of California at San Diego, La Jolla, USA) tested the link between cannabis use and psychosis among participants in the Cognitive Assessment and Risk Evaluation (CARE) Program.

CARE is a longitudinal program for individuals deemed to be at risk for developing a psychotic disorder, based on the presence of subsyndromal psychotic symptoms, a family history of schizophrenia, and/or a recent deterioration in global functioning.

During 1 year of follow-up, six (12.5%) of the 48 patients made the transition to psychosis. The transition rate was 3.1% among participants reporting no or minimal cannabis use versus 31.3% among those who met criteria for cannabis abuse or dependence.

The difference between cannabis users and non-users was statistically significant, Kristensen and Cadenhead report in the journal Psychiatry Research.

Further analyses found no association between alcohol or cocaine use and the conversion to psychosis; in contrast, nicotine use was significantly tied to later development of psychosis.

The authors admit that their findings are limited by the small sample size and reliance on self-reported measures of cannabis use. They call for future studies to address these limitations.

"Psychoeducation regarding the deleterious effects of cannabis use in vulnerable individuals could discourage use, and perhaps improve outcome," they conclude.

Psychiatry Research 2007; 151: 151-154

Cannabis abuse and risk for psychosis in a
prodromal sample

Karin Kristensen, Kristin S. Cadenhead

Department of Psychiatry, 0810, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0810, USA


The goal of the present study was to examine the rate of cannabis use among participants in the Cognitive Assessment and Risk Evaluation (CARE) Program, a longitudinal program for individuals who are “at risk” for developing a psychotic disorder. Cannabis abuse was assessed in 48 individuals identified as at risk for psychosis based on subsyndromal psychotic symptoms and/or family history. At 1 year follow-up, 6 of the 48 (12.5%) at risk subjects had made the transition to psychosis. Of the 32 subjects who had no use or minimal cannabis use, one subject (3.1%) converted to psychosis. Of the 16 subjects who met criteria for cannabis abuse/dependence, five (31.3%) converted to psychosis. The results show a significant association between cannabis abuse and conversion to psychosis in this sample. Nicotine use was also found to be significantly associated with later conversion. The significant associations between cannabis and nicotine abuse and conversion to psychosis in individuals at risk for schizophrenia suggest that early identification and intervention programs should screen for and provide education about the deleterious effects of these substances.

Winston De La Haye, M.D., M.P.H.   
Lecturer and Consultant Psychiatrist 
Department of Community Health & Psychiatry
The University of the West Indies, Mona, JAMAICA