Prospective study of cannabis use in adolescents at clinical high risk for psychosis: impact on conversion to psychosis and functional outcome

Background: Clinical and epidemiological studies suggest an association between cannabis use and psychosis but this relationship remains controversial.

Method: Clinical high-risk (CHR) subjects (age 12–22 years) with attenuated positive symptoms of psychosis (CHR+,n=101) were compared to healthy controls (HC,n=59) on rates of substance use, including cannabis. CHR+ subjects with and without lifetime cannabis use (and abuse) were compared on prodromal symptoms and social/role functioning at baseline. Participants were followed an average of 2.97 years to determine psychosis conversion status and functional outcome.

Results: At baseline, CHR+ subjects had significantly higher rates of lifetime cannabis use than HC. CHR+ lifetime cannabis users (n=35) were older (p=0.015, trend), more likely to be Caucasian (p=0.002), less socially anhedonic (p<0.001) and had higher Global Functioning: Social (GF:Social) scores (p<0.001) than non-users (n=61). CHR+ cannabis users continued to have higher social functioning than non-users at follow-up (p<0.001) but showed no differences in role functioning. A small sample of CHR+ cannabis abusers (n=10) showed similar results in that abusers were older (p=0.008), less socially anhedonic (p=0.017, trend) and had higher baseline GF:Social scores (p=0.006) than non-abusers. Logistic regression analyses revealed that conversion to psychosis in CHR+ subjects (n=15) was not related to lifetime cannabis use or abuse.

Conclusions: The current data do not indicate that low to moderate lifetime cannabis use is a major contributor to psychosis or poor social and role functioning in clinical high-risk youth with attenuated positive symptoms of psychosis.