A systematic review of 11 studies found no clear evidence that cannabis use causes additional cognitive impairment in youth with ADHD, though the studies were small and potentially underpowered.
Youth with ADHD who use cannabis, parents, psychiatrists, neurodevelopmental researchers
No additive ADHD x cannabis interaction found on executive function tasks
What the researchers found
No study found an additive or interaction effect between ADHD and cannabis use on neuropsychological tasks of executive function. Neuroimaging revealed differential brain activation and morphological differences in cannabis-using ADHD youth, but two studies found adverse impacts specifically from early-onset cannabis use.
Why it matters
Youth with ADHD are at elevated risk for cannabis use, making it critical to understand whether cannabis compounds their existing cognitive and neurological vulnerabilities. The current evidence, while limited, does not clearly support this hypothesis.
The numbers in context
11 studies identified; 7 used neuroimaging (fMRI, structural MRI, SPECT); differential activation in hippocampus, cerebellar vermis, temporal lobes; morphological differences in nucleus accumbens, frontal and postcentral gyri
How the study worked
Systematic review following PRISMA guidelines, searching four databases through January 2020. Eleven studies comparing ADHD youth with and without cannabis use were identified, seven using neuroimaging.
What this study cannot tell us
Most studies were small and potentially underpowered to detect interaction effects. Cross-sectional designs cannot establish causation. No standardized assessment protocols across studies.
How to read the evidence
Systematic review limited by small, heterogeneous, and potentially underpowered studies
When this study was published
Published in 2021. Research on cannabis effects specific to ADHD populations remains sparse.
The bigger picture
The lack of clear additive harm from cannabis on ADHD cognition is surprising given concerns about this population, but the very limited evidence base means this could change as larger studies are conducted.
Questions still open
- Are the brain differences in cannabis-using ADHD youth clinically meaningful? Does ADHD medication use modify the effects of cannabis on the brain? Would larger studies reveal additive effects not detected in small samples?
Common questions
Does cannabis make ADHD worse?
Should youth with ADHD be more concerned about cannabis?
Read the original research
Neurodevelopmental Effects of Cannabis Use in Adolescents and Emerging Adults with ADHD: A Systematic Review.
Harvard review of psychiatry, 29(4), 251-261
Citation
Cawkwell, Philip B; Hong, David S; Leikauf, John E. (2021). Neurodevelopmental Effects of Cannabis Use in Adolescents and Emerging Adults with ADHD: A Systematic Review.. Harvard review of psychiatry, 29(4), 251-261. https://doi.org/10.1097/HRP.0000000000000303
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