Conflicting Conclusions on Cannabis Use and Cognition in Schizophrenia

Published literature has associated cannabis use in patients with schizophrenia with worsened psychosis and transient cognitive effects. However, more recent studies have observed improvements in psychosis and cognition after short-term cannabinoid therapy.

To address this discrepancy, Jeff Jin, MD, and colleagues evaluated the effects of chronic cannabis use in patients with schizophrenia based on changes in specific cognitive domain scores from the Montreal Cognitive Assessment (MoCA), including attention, abstraction, and orientation. Their findings were presented at the American Psychiatric Association 2023 Annual Meeting.

Interestingly, researchers found a moderate-to-strong positive association between cannabis use and MoCA scores and identified duration of cannabis use as a significant independent predictive factor in this relationship. Furthermore, the strongest association observed in the study was between frequent lifetime cannabis use and abstraction domain MoCA scores.

The cross-sectional study enrolled a cohort of 31 inpatients (mean age, 30.52±2.95 years; 87% male) with schizophrenia diagnosed per Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition criteria. In addition to MoCA assessments, researchers used the Cannabis Abuse Screening Test (CAST) and the Kreek-McHugh-Schluger-Kellogg (KMSK) cannabis scale to characterize participants’ 30-day and lifetime cannabis use.

Using Pearson correlation tests, authors found a strong positive association between duration of lifetime cannabis use and total MoCA scores (R=.497; P=.001). Furthermore, lifetime cannabis use duration was moderately positively associated with attention (R=.440; P=.028), abstraction (R=.458; P=.021), and orientation (R=.567; P=.003).

Likewise, lifetime cannabis use frequency showed moderate positive associations with total (R=.432; P=.031), abstraction (R=.497; P=0.011), and orientation (R=.436; P=.029) MoCA scores. Researchers also observed 30-day cannabis duration was associated with language MoCA scores (R=.429; P=.032), and lifetime cannabis duration was associated with total and abstraction MoCA scores (R=.552; P=.004); however, these associations were no longer significant after adjusting for education.

Ultimately, investigators suggested that “these positive associations between chronic cannabis use and cognition raise further questions around the true long-term effects of cannabis in patients with schizophrenia and warrant further investigation.”