After 3 months of medical marijuana treatment, patients showed improved executive function task performance, brain activation patterns that looked more like healthy controls, and notable decreases in opioid and benzodiazepine use.
Read this if you want to understand how medical marijuana affects brain function differently from recreational use.
Brain activation moved toward healthy norms after 3 months of medical marijuana
What the researchers found
Medical marijuana patients were assessed before starting treatment and after 3 months using fMRI while performing the Multi-Source Interference Test (MSIT). After treatment, patients showed improved task performance accompanied by changes in brain activation in the cingulate cortex and frontal regions.
Remarkably, brain activation patterns after treatment appeared more similar to those of healthy controls from previous studies than at pre-treatment, suggesting potential normalization of brain function. This contrasts sharply with recreational cannabis research, which typically shows worsened performance and altered brain activation.
Patients also reported improvements in clinical symptoms and health measures, and notable decreases in prescription medication use, particularly opioids and benzodiazepines.
Why it matters
This is one of the first studies to directly measure brain function changes in medical marijuana patients over time. The finding that medical use may improve rather than impair executive function directly challenges the assumption that all cannabis use degrades cognition. The opioid and benzodiazepine reduction adds practical clinical significance.
The numbers in context
Improved MSIT performance after 3 months. Brain activation changes in cingulate cortex and frontal regions. Activation patterns moved toward healthy control norms. Notable decreases in opioid and benzodiazepine prescriptions.
How the study worked
Longitudinal observational study of medical marijuana patients assessed before initiating treatment and after 3 months. fMRI during the MSIT captured brain activation changes. Clinical state, health measures, and prescription medication use were also tracked.
What this study cannot tell us
Small pilot study without a control group. Improvement could reflect placebo effects, practice effects on repeated testing, or improvement in underlying conditions. The comparison to healthy controls is from previous studies, not matched. No randomization or blinding. Short follow-up period.
How to read the evidence
Longitudinal observational study with fMRI. Innovative but uncontrolled and small, limiting causal conclusions.
When this study was published
Published in 2017. This is from an ongoing longitudinal study that has continued to publish findings on medical marijuana and cognition.
The bigger picture
The contrast between medical and recreational cannabis effects on the brain is striking. Medical patients may be self-treating conditions (pain, anxiety) that were already impairing their cognition. Effective symptom relief through medical cannabis could remove that cognitive burden, explaining the improvement. This distinction between medical and recreational contexts may be one of the most important in cannabis research.
Questions still open
- Would a larger controlled trial confirm these improvements? Is the cognitive improvement driven by pain relief, sleep improvement, or reduced use of other medications? Do the improvements persist with longer-term medical marijuana use?
Common questions
How can medical marijuana improve cognition when recreational marijuana impairs it?
Did patients stop taking opioids?
Read the original research
The Grass Might Be Greener: Medical Marijuana Patients Exhibit Altered Brain Activity and Improved Executive Function after 3 Months of Treatment.
Frontiers in pharmacology, 8, 983
Citation
Gruber, Staci A; Sagar, Kelly A; Dahlgren, Mary K; Gonenc, Atilla; Smith, Rosemary T; Lambros, Ashley M; Cabrera, Korine B; Lukas, Scott E. (2017). The Grass Might Be Greener: Medical Marijuana Patients Exhibit Altered Brain Activity and Improved Executive Function after 3 Months of Treatment.. Frontiers in pharmacology, 8, 983. https://doi.org/10.3389/fphar.2017.00983
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