MS Patients Who Used Cannabis Showed More Cognitive Impairment and Altered Brain Activity
Multiple sclerosis patients who smoked cannabis performed worse on cognitive tests and showed more diffuse brain activation patterns than non-using MS patients.
Quick Facts
What This Study Found
Compared to matched MS patients who did not use cannabis, cannabis-using MS patients performed significantly worse on two cognitive measures: the more demanding version of the Paced Auditory Serial Addition Test (processing speed) and the 10/36 Spatial Recall Test (visual memory).
On fMRI during a working memory task, cannabis users showed more diffuse cerebral activation across all difficulty levels and made more errors on the most demanding task. During the hardest condition, cannabis users showed increased activation in parietal and anterior cingulate regions involved in working memory, suggesting they needed to recruit more brain resources to attempt the same tasks.
No group differences were found in resting-state brain networks or structural MRI measures (lesion volumes, brain tissue volumes, or white matter integrity), meaning the functional differences were not explained by greater structural brain damage in cannabis users.
Key Numbers
20 cannabis users and 19 non-users with MS. Cannabis users performed worse on PASAT 2-second (p<0.02) and 10/36 Spatial Recall (p<0.03). More errors on 2-Back task (p<0.006). Increased parietal (p<0.007) and anterior cingulate (p<0.001) activation during demanding working memory tasks.
How They Did This
Twenty MS patients who smoked cannabis and 19 non-using MS patients, matched on demographic and neurological variables, underwent fMRI during a working memory task (N-Back), resting-state fMRI, and structural MRI (including diffusion tensor imaging). A comprehensive neuropsychological battery assessed verbal memory, visual memory, processing speed, and attention.
Why This Research Matters
MS already compromises cognitive function through brain inflammation and damage. This study suggests cannabis use may compound these cognitive problems by further disrupting the brain's compensatory mechanisms. For MS patients considering cannabis for symptom management, these cognitive trade-offs are important to understand.
The Bigger Picture
MS patients often use cannabis for pain, spasticity, and sleep. However, this study indicates that cannabis use may worsen the cognitive difficulties that are already common in MS. The finding that cannabis disrupts the brain's compensatory activation patterns, without additional structural damage, suggests a functional mechanism that could potentially be reversible with cessation.
What This Study Doesn't Tell Us
This was a cross-sectional study, so it cannot determine whether cannabis caused the cognitive differences or whether individuals with more cognitive difficulties were more likely to use cannabis. The cannabis users were assessed in an unintoxicated state, but chronic effects may differ from acute effects. The sample size was small (20 users, 19 non-users).
Questions This Raises
- ?Are the cognitive effects reversible with cannabis cessation?
- ?Do different cannabis products (e.g., CBD-dominant) have different cognitive impacts in MS?
- ?How should clinicians weigh symptom relief against cognitive risks when counseling MS patients about cannabis?
Trust & Context
- Key Stat:
- Cannabis users needed more brain activation to attempt working memory tasks and still made more errors
- Evidence Grade:
- This is a well-designed cross-sectional study with neuroimaging and neuropsychological data, but the sample size was small and the design cannot establish causation.
- Study Age:
- Published in 2014. Research on cannabis and cognition in MS continues as cannabis use becomes more common in this population.
- Original Title:
- Effects of cannabis on cognition in patients with MS: a psychometric and MRI study.
- Published In:
- Neurology, 82(21), 1879-87 (2014)
- Authors:
- Pavisian, Bennis(4), MacIntosh, Bradley J, Szilagyi, Greg, Staines, Richard W, O'Connor, Paul, Feinstein, Anthony
- Database ID:
- RTHC-00848
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
What does "more diffuse activation" mean?
In healthy brains, specific tasks activate specific brain regions efficiently. In MS, the brain compensates for damage by recruiting additional regions. Cannabis users showed even more widespread activation, suggesting cannabis further disrupts the brain's ability to process information efficiently.
Were the cannabis users intoxicated during testing?
No. Testing was conducted in an unintoxicated state. The findings reflect chronic effects of regular cannabis use on brain function rather than acute intoxication effects.
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Cite This Study
https://rethinkthc.com/research/RTHC-00848APA
Pavisian, Bennis; MacIntosh, Bradley J; Szilagyi, Greg; Staines, Richard W; O'Connor, Paul; Feinstein, Anthony. (2014). Effects of cannabis on cognition in patients with MS: a psychometric and MRI study.. Neurology, 82(21), 1879-87. https://doi.org/10.1212/WNL.0000000000000446
MLA
Pavisian, Bennis, et al. "Effects of cannabis on cognition in patients with MS: a psychometric and MRI study.." Neurology, 2014. https://doi.org/10.1212/WNL.0000000000000446
RethinkTHC
RethinkTHC Research Database. "Effects of cannabis on cognition in patients with MS: a psyc..." RTHC-00848. Retrieved from https://rethinkthc.com/research/pavisian-2014-effects-of-cannabis-on
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.