Adult psychosis patients (i.e. over the age of 25 years) who are also lifetime cannabis users (CANN+/-) appear to exhibit superior cognition compared to never-using patients (CANN-). The objective of this meta-analysis was to evaluate the cognitive differences between CANN- and patients who currently use cannabis (CANN+) (i.e. during the CANN ± patients’ cannabis-using stage). Specifically, focusing on young patients under the age of 25 years, the typical stage of both psychosis- and cannabis-onset.
Of the 308 studies identified through database searches and secondary referencing, 14 compared neurocognition of CANN+ and CANN- in young people with psychotic disorders (mean age between 15 and 45 years). Effect sizes were extracted using neurocognitive test performance between CANN+ and CANN- and random effects modelling was conducted on pooled ES and moderator analyses.
CANN + performed worse on several cognitive domains (i.e. premorbid IQ, current IQ, verbal learning, verbal working memory, motor inhibition) compared to CANN-. The association between age and performance in CANN + cognition was varied, with older age predictive of worse performance in processing speed, sustained attention, verbal memory, and better performance in verbal learning and very fluency. Of note, CANN + outperformed CANN- in tests of conceptual set-shifting.
These results are consistent with previous findings indicating that CANN + (users of cannabis) demonstrate poorer neurocognition than CANN-; and that this is exacerbated with increasing age. Our findings demonstrate significant cognitive differences between patients with CANN + versus CANN- even at early-onset psychosis, which could suggest a different underlying mechanism towards psychosis for cannabis users.
Young people, Schizophrenia, Early-onset psychosis, Cognition, Marijuana, Comorbidity