Pre-illness cannabis use and the early course of nonaffective psychotic disorders: associations with premorbid functioning, the prodrome, and mode of onset of psychosis.

Introduction: Limited research indicates that pre-illness cannabis use may result in an earlier age at onset of psychosis, though little is known about the influence of prior cannabis use on the premorbid and prodromal phases. This study examined the effects of prior or concurrent cannabis (as well as nicotine and alcohol) use on: (1) early adolescent (12-15 years) premorbid functioning, (2) late adolescent (16-18 years) premorbid functioning, (3) two features of the prodrome, and (4) mode of onset of psychosis.

Methods: Participants included 109 well-characterized first-episode patients hospitalized in public-sector settings. Assessments included ages at initiation of first, weekly, and daily use of substances, the Premorbid Adjustment Scale, the Symptom Onset in Schizophrenia inventory, and a consensus-based best estimate of mode of onset.

Results: Participants having used cannabis at ≤15 years had better early adolescence social functioning than those who had not used cannabis (p=0.02). Conversely, those who had used cannabis at ≤18 years had poorer late adolescence academic functioning (p<0.001). Participants having used cannabis before onset of psychotic symptoms did not differ from those who had not in terms of having had an identifiable prodrome or the number of prodromal symptoms experienced. Whereas 42% of those having used cannabis daily had an acute mode of onset of psychosis, only 20% of those without prior daily cannabis use had an acute onset (p=0.04).

Conclusions: Findings suggest that cannabis use is associated with premorbid social and academic functioning and mode of onset. Further research is warranted to elucidate the complex associations between cannabis use and diverse early-course features.