Limited evidence does not clearly show cannabis worsens brain outcomes in youth with ADHD
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- No additive ADHD x cannabis interaction found on executive function tasks
- Evidence Grade:
- Systematic review limited by small, heterogeneous, and potentially underpowered studies
- Study Age:
- Published in 2021. Research on cannabis effects specific to ADHD populations remains sparse.
- Original Title:
- Neurodevelopmental Effects of Cannabis Use in Adolescents and Emerging Adults with ADHD: A Systematic Review.
- Published In:
- Harvard review of psychiatry, 29(4), 251-261 (2021)
- Authors:
- Cawkwell, Philip B, Hong, David S, Leikauf, John E
- Database ID:
- RTHC-03050
Evidence Hierarchy
Analyzes all available research on a topic using a structured method.
What do these levels mean? →Frequently Asked Questions
Does cannabis make ADHD worse?
Current evidence does not clearly show that cannabis causes additional cognitive impairment in youth with ADHD beyond what either condition causes alone. However, the studies are small and more research is needed.
Should youth with ADHD be more concerned about cannabis?
Youth with ADHD are at elevated risk for substance use. While this review did not find clear additive cognitive harm, two studies found adverse effects from early-onset cannabis use, suggesting earlier use may be more concerning.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-03050APA
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
MLA
Cawkwell, Philip B, et al. "Neurodevelopmental Effects of Cannabis Use in Adolescents and Emerging Adults with ADHD: A Systematic Review.." Harvard review of psychiatry, 2021. https://doi.org/10.1097/HRP.0000000000000303
RethinkTHC
RethinkTHC Research Database. "Neurodevelopmental Effects of Cannabis Use in Adolescents an..." RTHC-03050. Retrieved from https://rethinkthc.com/research/cawkwell-2021-neurodevelopmental-effects-of-cannabis
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.