Schizophrenia patients who used cannabis showed better brain processing than those who did not | Research

The takeaway

Schizophrenia patients with cannabis use disorder showed greater mismatch negativity (MMN) amplitudes than schizophrenia patients without cannabis use, with levels comparable to healthy controls.

Psychosis researchers, neuroscientists, and clinicians studying the cannabis-cognition-psychosis relationship.

Cannabis-using schizophrenia patients had MMN comparable to healthy controls

What the researchers found

Schizophrenia patients without cannabis use showed reduced frontocentral MMN to duration deviants compared to healthy controls, as expected. However, schizophrenia patients with comorbid cannabis use showed greater MMN amplitudes than non-using patients, with no significant difference from healthy controls.

Why it matters

This counterintuitive finding suggests that schizophrenia patients who use cannabis may represent a cognitively less impaired subgroup, rather than cannabis protecting the brain. It challenges simple assumptions about cannabis always worsening cognition in psychosis.

The numbers in context

20 schizophrenia patients without CUD, 21 with CUD, 20 healthy controls. Schizophrenia + CUD patients had greater MMN amplitudes than non-CUD patients at central electrodes.

How the study worked

Cross-sectional EEG study comparing 20 schizophrenia patients without CUD, 21 with CUD, and 20 healthy controls. Auditory oddball paradigm measured MMN to frequency and duration deviants.

What this study cannot tell us

Small cross-sectional study; cannot determine causation. The design cannot distinguish whether cannabis improved cognition or whether less impaired patients are more likely to use cannabis.

How to read the evidence

Preliminary: small cross-sectional EEG study with limited sample per group.

When this study was published

Published in 2019.

The bigger picture

One interpretation is that cognitively better-functioning schizophrenia patients are more capable of obtaining and using cannabis. This would mean the association reflects patient characteristics rather than a cannabis benefit.

Questions still open

Is this a selection effect (less impaired patients use more cannabis) or a cannabis effect (cannabis use preserves some cognitive function)? Would longitudinal studies clarify the direction of causation?

Common questions

What is mismatch negativity?

MMN is an automatic brain response when an unexpected sound occurs in a series of regular sounds. It reflects the brain's ability to detect changes and is typically reduced in schizophrenia, indicating impaired pre-attentive processing.

Does this mean cannabis helps cognition in schizophrenia?

Not necessarily. The authors suggest the more likely explanation is that less cognitively impaired patients are more likely to seek out and use cannabis, rather than cannabis improving their brain function.

Read the original research

Impact of Chronic Cannabis Use on Auditory Mismatch Negativity Generation in Schizophrenia Patients.

Pharmacopsychiatry, 52(3), 126-133

View on PubMed ↗Publisher’s paper ↗

Citation

Roser, Patrik; Pichler, Eva-Maria; Habermeyer, Benedikt; Kawohl, Wolfram; Juckel, Georg. (2019). Impact of Chronic Cannabis Use on Auditory Mismatch Negativity Generation in Schizophrenia Patients.. Pharmacopsychiatry, 52(3), 126-133. https://doi.org/10.1055/a-0573-9866