Clinical and epidemiological studies suggest an association between cannabis use and psychosis, but this relationship remains controversial.
Clinical High-Risk (CHR) subjects (age 12–22) 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.
At baseline, CHR+ subjects had significantly higher rates of lifetime cannabis use than HC subjects. CHR+ lifetime cannabis users (N=35) were older (p=0.015, trend), more likely Caucasian (p=0.002), less socially anhedonic (p<0.001), and had higher Global Functioning (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 no differences on 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.
The current data do not support low to moderate lifetime cannabis use to be a major contributor to psychosis or poor social and role functioning in high-risk youth.