Schizophrenia Patients Who Used Cannabis Actually Had Better Cognitive Function Than Non-Users | Research

The takeaway

A meta-analysis of 10 studies plus new first-episode data found that schizophrenia patients with a history of cannabis use performed better on cognitive tests than non-using patients, possibly because they needed less cognitive vulnerability to develop psychosis.

Read this if you want to understand the surprising cognitive findings in cannabis-using schizophrenia patients.

Cannabis-using psychosis patients outperformed non-users on working memory and executive function

What the researchers found

In a surprising finding that contradicts common assumptions, the meta-analysis of 572 patients found that those with a history of cannabis use had superior neuropsychological functioning compared to non-using schizophrenia patients. This was primarily driven by studies including patients with lifetime (rather than current) cannabis history.

A second study of 85 first-episode psychosis (FEP) patients confirmed the pattern: cannabis-using FEP patients showed only selective cognitive impairments while non-users showed generalized deficits. Cannabis users performed better on visual memory, working memory, and executive functioning. Patients who started cannabis earlier had even less cognitive impairment.

Why it matters

This counterintuitive finding has an important implication: cannabis-using patients who develop psychosis may represent a "cognitively less impaired" subgroup who needed an environmental trigger (cannabis) to develop psychosis. Non-using patients may have developed psychosis due to greater underlying cognitive vulnerability, without needing an external trigger.

The numbers in context

Meta-analysis: 10 studies, 572 patients. FEP study: 59 cannabis users vs. 26 non-users vs. 43 controls. Cannabis users outperformed non-users on visual memory, working memory, and executive functioning. Earlier cannabis onset associated with less cognitive impairment.

How the study worked

Two-part study. Study I: Meta-analysis of 10 studies comprising 572 patients with established schizophrenia. Study II: Neuropsychological testing of 85 first-episode psychosis patients (59 cannabis users, 26 non-users) and 43 healthy controls.

What this study cannot tell us

The meta-analysis included mostly cross-sectional studies. Better cognition in cannabis users could reflect selection bias (more cognitively intact people are more likely to access and use cannabis). Lifetime cannabis history includes people who stopped years ago. The sample sizes, while reasonable for a meta-analysis, are modest.

How to read the evidence

Meta-analysis of 10 studies plus a new first-episode sample; strong evidence for the cognitive difference, though causation remains unclear.

When this study was published

Published in 2012. The "neurocognitively less impaired" hypothesis for cannabis-using psychosis patients has been further investigated since.

The bigger picture

This research reshapes understanding of the cannabis-psychosis relationship. Rather than cannabis universally worsening cognitive outcomes in psychosis, it appears that the people who develop psychosis after cannabis use may be fundamentally different, cognitively stronger, than those who develop it without cannabis exposure.

Questions still open

Does the cognitive advantage of cannabis-using patients persist over the long term? Does this finding change how cannabis-using psychosis patients should be treated? Could cognitive testing help predict which cannabis users are at genuine psychosis risk?

Common questions

How can cannabis users with psychosis have better cognition?

The leading explanation is that cannabis-using psychosis patients started with better baseline cognitive function. They may have needed the additional risk from cannabis to push them into psychosis, whereas non-using patients had enough underlying vulnerability to develop psychosis without any environmental trigger. Cannabis use in this model is a marker of less inherent vulnerability, not a cause of better cognition.

Does this mean cannabis is good for people with schizophrenia?

No. The study does not show that cannabis improves cognition in schizophrenia. Rather, it suggests that people who develop psychosis after cannabis use may represent a distinct subgroup with better baseline cognitive abilities. Cannabis use in schizophrenia is still associated with poor treatment compliance and psychotic relapse.

Read the original research

The impact of cannabis use on cognitive functioning in patients with schizophrenia: a meta-analysis of existing findings and new data in a first-episode sample.

Schizophrenia bulletin, 38(2), 316-30

View on PubMed ↗Publisher’s paper ↗

Citation

Yücel, Murat; Bora, Emre; Lubman, Dan I; Solowij, Nadia; Brewer, Warrick J; Cotton, Sue M; Conus, Philippe; Takagi, Michael J; Fornito, Alex; Wood, Stephen J; McGorry, Patrick D; Pantelis, Christos. (2012). The impact of cannabis use on cognitive functioning in patients with schizophrenia: a meta-analysis of existing findings and new data in a first-episode sample.. Schizophrenia bulletin, 38(2), 316-30. https://doi.org/10.1093/schbul/sbq079