Long-Term Cannabis Use Affected Attention Differently in People With and Without Schizophrenia
Chronic cannabis use was associated with reduced attention-related brain responses in healthy people but not in people with schizophrenia, suggesting the two groups may have fundamentally different endocannabinoid systems.
Quick Facts
What This Study Found
Researchers measured attention-related brainwave responses (P300) in four groups: schizophrenia patients with and without chronic cannabis use, and healthy controls with and without chronic cannabis use. All cannabis users had been abstinent for at least 28 days.
As expected, schizophrenia patients overall showed reduced P300 responses. But the cannabis effect was unexpected: chronic cannabis use was associated with reduced P300 responses in the healthy control group, but not in the schizophrenia group.
In healthy cannabis users, the P300 reduction correlated with both the amount and duration of cannabis use. In schizophrenia patients who used cannabis, no such correlation existed. The P300 differences between cannabis users and non-users in the healthy group were statistically significant, while the schizophrenia group showed no significant difference.
Key Numbers
80 participants in 4 groups of 20. Mean cannabis use: 8.3 years (schizophrenia group), 9.1 years (controls). Minimum 28 days abstinent. Healthy cannabis users showed dose-dependent left-hemispheric P300 reduction (r = -0.50 for amount, r = -0.57 for duration).
How They Did This
The study used auditory novelty and oddball P300 evoked potential paradigms in 80 participants divided into four groups of 20: schizophrenia with chronic cannabis use (abstinent 28+ days), schizophrenia without, healthy controls with chronic cannabis use (abstinent 28+ days), and healthy controls without. Mean duration of regular cannabis use was 8.3 years (schizophrenia group) and 9.1 years (control group).
Why This Research Matters
The finding that cannabis affects attention differently in people with and without schizophrenia has a provocative implication: it suggests the endocannabinoid system may already be altered in schizophrenia, making it less responsive to additional cannabinoid insult. This aligns with theories that endocannabinoid dysfunction is part of schizophrenia's underlying biology.
The Bigger Picture
The relationship between cannabis and schizophrenia is often framed as cannabis causing psychosis. This study adds nuance by showing that cannabis affects the brains of people with schizophrenia differently than healthy brains, suggesting pre-existing neurobiological differences that may influence both vulnerability to psychosis and response to cannabis.
What This Study Doesn't Tell Us
Cross-sectional design cannot establish causation. The 28-day abstinence requirement may not fully eliminate residual cannabis effects. The study included both first-episode and chronic schizophrenia patients, mixing different illness stages. The sample size (20 per group) limits statistical power.
Questions This Raises
- ?Is the endocannabinoid system already dysfunctional in schizophrenia, making cannabis effects different?
- ?Do the attention deficits in healthy cannabis users resolve with longer abstinence?
- ?Could P300 measurements be used to identify cannabis-related cognitive risk?
Trust & Context
- Key Stat:
- Cannabis-related attention deficits correlated with use duration in healthy users (r = -0.57) but not in schizophrenia patients.
- Evidence Grade:
- Moderate evidence from a well-controlled neurophysiology study with appropriate comparison groups, though limited by sample size and cross-sectional design.
- Study Age:
- Published in 2016. The endocannabinoid dysfunction hypothesis in schizophrenia continues to be investigated.
- Original Title:
- Attentional dysfunction in abstinent long-term cannabis users with and without schizophrenia.
- Published In:
- European archives of psychiatry and clinical neuroscience, 266(5), 409-21 (2016)
- Authors:
- Rentzsch, Johannes(3), Stadtmann, Ada(2), Montag, Christiane(2), Kunte, Hagen, Plöckl, Doris, Hellweg, Rainer, Gallinat, Jürgen, Kronenberg, Golo, Jockers-Scherübl, Maria Christiane
- Database ID:
- RTHC-01248
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Does cannabis affect the brain the same way in everyone?
No. This study found cannabis had different effects on attention-related brain responses depending on whether the person had schizophrenia. Healthy cannabis users showed dose-dependent attention deficits that were absent in cannabis users with schizophrenia.
Does this mean cannabis is safer for people with schizophrenia?
No. The finding that cannabis affects the brain differently in schizophrenia does not mean the effects are benign. It may instead reflect that the endocannabinoid system is already disrupted in schizophrenia, potentially contributing to the condition itself.
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Cite This Study
https://rethinkthc.com/research/RTHC-01248APA
Rentzsch, Johannes; Stadtmann, Ada; Montag, Christiane; Kunte, Hagen; Plöckl, Doris; Hellweg, Rainer; Gallinat, Jürgen; Kronenberg, Golo; Jockers-Scherübl, Maria Christiane. (2016). Attentional dysfunction in abstinent long-term cannabis users with and without schizophrenia.. European archives of psychiatry and clinical neuroscience, 266(5), 409-21. https://doi.org/10.1007/s00406-015-0616-y
MLA
Rentzsch, Johannes, et al. "Attentional dysfunction in abstinent long-term cannabis users with and without schizophrenia.." European archives of psychiatry and clinical neuroscience, 2016. https://doi.org/10.1007/s00406-015-0616-y
RethinkTHC
RethinkTHC Research Database. "Attentional dysfunction in abstinent long-term cannabis user..." RTHC-01248. Retrieved from https://rethinkthc.com/research/rentzsch-2016-attentional-dysfunction-in-abstinent
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.