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.