The Longitudinal Impact of Cannabis Use On Cognitive Functioning in First Episode Psychosis

Background and Purpose: Cannabis is a commonly used illicit drug in early course schizophrenia and other psychotic disorders. Despite the known associations between cannabis and its negative effects on cognitive functioning in healthy individuals, research on its impact in schizophrenia has surprisingly suggested an association between cannabis use and improved cognition in people with psychotic conditions. Despite these findings, cognitive impairments are core features of psychosis and cannabis abuse is a problem that profoundly limits recovery from psychiatric disability. Further, most studies have only observed cognitive correlates of cannabis use in cross-sectional samples. Examining cannabis use over time may show exacerbations in cognitive dysfunction in the condition, which could have implications for social work development efforts.  This study investigated the longitudinal impact of cannabis use on cognition in first episode neuroleptic naïve persons with psychosis. 

Methods: A total of 183 first episode neuroleptic naïve participants with psychosis were recruited through Western Psychiatric Institute and Clinic, Pittsburgh. Participants were enrolled and followed 1-year from their first psychotic episode. Of those enrolled, 41 (22%) used cannabis over the 1-year follow-up period.  The computerized version of the Wisconsin Card Sorting Test was used to assess executive functioning (WSCT) at baseline, 6-months and 1-year. Linear growth curve models were used to examine 1-year executive functional outcome trajectories between the cannabis misusing and non-cannabis using participants with psychosis.

Results: The differences in WSCT percent perseverative errors score changes between first episode participants who used cannabis and the non-cannabis users were examined. Over 1-year, the effects of cannabis on cognition in schizophrenia were readily discernible between participant groups. Contrary to our expectations, participants who used cannabis exhibited significantly faster improvement in executive functioning compared to those not using cannabis, F (1, 130) = 4.55, p = .035, comparatively. These results show that the first-episode participants who used cannabis experienced slightly greater improvements in cognitive functioning following their first-episode of psychosis, which may account for cross-sectional studies demonstrating greater cognitive abilities in participants with psychosis who use cannabis.

Conclusions and Implications: The clinical relevance of this research is underscored by the fact that this was the first study to examine the longitudinal effects of cannabis use on cognition in first-episode psychosis. Our sample was clinically homogenous, and presented without the confounding effects of illness chronicity and neuroleptic medications on cognition. Despite our expectations, the use of cannabis was associated with a more rapid decrease in executive impairments after the introduction of antipsychotic medication. This may be due to elevated initial rates or a different pathogenesis of cognitive dysfunction among cannabis users that may be more responsive to traditional pharmacotherapy. The clinical correlates of cannabis have not been thoroughly examined in first-episode psychosis, and it will be important for social work to secure an integral role in future research development efforts.