Chronic cannabis use impaired a measure of brain signal filtering (P200 suppression) in healthy people but paradoxically improved it in schizophrenia patients, suggesting the endocannabinoid system functions differently in schizophrenia.
Readers interested in why cannabis affects people with schizophrenia differently.
Cannabis improved P200 suppression in schizophrenia (p < 0.02) but impaired it in healthy controls (p < 0.02)
What the researchers found
Researchers measured how the brain filters repeated auditory signals in four groups: schizophrenia patients with and without cannabis use, and healthy controls with and without cannabis use. They focused on "repetition suppression," where the brain normally dampens its response to a repeated sound.
For the P200 brain wave component, cannabis had opposite effects depending on diagnosis. In healthy controls, chronic cannabis use was associated with worse suppression (0.55 vs. 0.40, p < 0.02), meaning poorer signal filtering. In schizophrenia patients, cannabis use was associated with better suppression (0.36 vs. 0.54, p < 0.02), meaning improved signal filtering.
Among healthy controls, total lifetime cannabis consumption correlated with worse P200 suppression (r = 0.28, p < 0.007). Among schizophrenia patients, longer time since last cannabis use correlated with worse P200 suppression (r = 0.42, p < 0.002), suggesting the benefit faded with abstinence.
Why it matters
This study provides neurophysiological evidence for the paradox of cannabis use in schizophrenia: while cannabis is a risk factor for psychosis, many patients report subjective benefits. The opposing effects on P200 suppression suggest that the endocannabinoid system may be fundamentally altered in schizophrenia, meaning cannabis interacts with a different neurological landscape in these patients.
The numbers in context
34 schizophrenia patients with cannabis, 33 without. 45 controls with cannabis, 61 without. Interaction between diagnosis and cannabis on P200 suppression: p < 0.001. Cannabis-using controls: suppression ratio 0.55. Non-using controls: 0.40. Cannabis-using schizophrenia: 0.36. Non-using schizophrenia: 0.54.
How the study worked
Mixed-sample study with 34 schizophrenia patients and 45 healthy controls who were chronic heavy cannabis users, plus 33 schizophrenia patients and 61 healthy controls without cannabis use. Auditory event-related potentials were recorded using a paired-stimulus paradigm measuring P50, N100, and P200 repetition suppression.
What this study cannot tell us
Cross-sectional design cannot determine causation. Cannabis users in both groups may differ from non-users in ways beyond cannabis exposure (other substance use, medication differences). P200 suppression is one of many possible measures of sensory processing, and its clinical relevance is debated. The study measured chronic heavy use and did not assess the effects of different doses or patterns of use.
How to read the evidence
Moderate evidence from a well-designed case-control study with adequate sample sizes, though limited by cross-sectional design.
When this study was published
Published in 2017. Contributes to understanding of endocannabinoid system alterations in schizophrenia.
The bigger picture
The relationship between cannabis and schizophrenia is not simply "cannabis causes psychosis." This study reveals that the neurobiological effects of cannabis differ fundamentally between healthy brains and brains affected by schizophrenia. This divergence likely reflects underlying alterations in the endocannabinoid system that are part of schizophrenia itself, not just a consequence of cannabis use.
Questions still open
- Could endocannabinoid system abnormalities in schizophrenia be a target for treatment? Does the paradoxical improvement in P200 suppression with cannabis in schizophrenia translate to any functional benefit? Would targeted cannabinoid therapies improve sensory processing in schizophrenia without the risks of cannabis use?
Common questions
Does this mean cannabis helps schizophrenia?
Why would cannabis have opposite effects in healthy versus schizophrenia brains?
Read the original research
Opposing Effects of Cannabis Use on Late Auditory Repetition Suppression in Schizophrenia Patients and Healthy Control Subjects.
Biological psychiatry. Cognitive neuroscience and neuroimaging, 2(3), 263-271
Citation
Rentzsch, Johannes; Kronenberg, Golo; Stadtmann, Ada; Neuhaus, Andres; Montag, Christiane; Hellweg, Rainer; Jockers-Scherübl, Maria Christiane. (2017). Opposing Effects of Cannabis Use on Late Auditory Repetition Suppression in Schizophrenia Patients and Healthy Control Subjects.. Biological psychiatry. Cognitive neuroscience and neuroimaging, 2(3), 263-271. https://doi.org/10.1016/j.bpsc.2016.10.004
Explore the wider topic
- How THC Affects Your Amygdala: The Brain's Threat Detector and Cannabis
- The Anandamide Connection: Your Body's Natural Bliss Molecule
- How Long for Cannabinoid Receptors to Return to Normal
- Cannabis and the Developing Brain: What Every Teenager (and Parent) Should Know
- Why Can't I Enjoy Anything Without Weed? The Science Behind It
- Dopamine Recovery After Quitting Weed: What the Science Says
- The Endocannabinoid System Explained Simply: What It Does and Why It Matters
- Your Endocannabinoid System Explained: Why Withdrawal Happens
- Your Nervous System After Quitting Weed: Fight or Flight
- Using Weed Under 18: What It Does to Your Developing Brain
- What THC Does to Your Brain: Why Withdrawal Happens
- THC and Your Prefrontal Cortex: What Cannabis Does to Your Decision-Making Brain
- Weed, Cortisol, and Stress: What Cannabis Does to Your Stress Hormones
- Weed and Memory: What the Science Says About THC and Your Hippocampus
- Weed and Motivation: Is Amotivational Syndrome Real?
- Weed and Your Nervous System: What THC Actually Does to Your Brain and Body
- How Weed Rewires Your Reward System (And How to Reset It)