New study reveals how chronic cannabis use impacts brain activation, with long-term effects on decision-making and memory, raising questions about its growing global popularity.
Study: Brain Function Outcomes of Recent and Lifetime Cannabis Use. Image Credit: Lightspring / Shutterstock
In a recent study published in the journal JAMA Network Open, a group of researchers investigated the associations between lifetime heavy cannabis use, recent use, and brain activation during cognitive tasks.
Background
As cannabis legalization expands globally, its use has surged, with nearly 200 million people consuming it annually. While many view cannabis as harmless, emerging evidence tells a different story.
Studies show that cannabis can impair memory, decision-making, and other critical cognitive functions, raising concerns about its long-term effects on brain health. This is particularly relevant in an era where cannabis potency has increased dramatically.
Despite prior research, knowledge gaps persist regarding how cannabis use—both recent and cumulative—affects different areas of brain function. This understanding is essential for public health policies and educational initiatives.
About the Study
The study utilized data from the Human Connectome Project and involved 1,003 adults aged 22–36. Participants underwent functional magnetic resonance imaging (fMRI) during tasks assessing working memory, emotion, reward, motor function, relational reasoning, theory of mind, and language processing.
Cannabis use was categorized into nonuser (fewer than 10 uses), moderate user (10–999 uses), or heavy user (1,000+ uses), based on self-reports through the Semi-Structured Assessment for the Genetics of Alcoholism. Recent use was determined via urine toxicology, with tetrahydrocannabinol (THC) metabolite levels serving as the indicator.
Linear mixed-effects regression models analyzed the relationship between cannabis use and brain activation. Confounders like age, sex, socioeconomic status, alcohol use, and nicotine dependence were controlled. Mean activation values from task-specific brain regions were used as primary metrics. Post-hoc analyses identified specific regions affected by heavy use, validated by excluding participants with recent use. Significance adjustments, such as the Benjamini-Hochberg correction, were applied to reduce false discovery rates and ensure robust findings.
Study Results
The study reveals important insights into the neural impacts of cannabis use, both recent and over a lifetime. Among participants, 8.8% reported heavy lifetime cannabis use, which was significantly associated with reduced brain activation during working memory tasks.
Key regions affected include the dorsolateral prefrontal cortex (dlPFC), dorsomedial prefrontal cortex (dmPFC), and anterior insula. These regions play critical roles in decision-making, planning, and higher-order cognitive functions, making these impairments particularly concerning for individuals engaged in complex, cognitively demanding activities.
Recent cannabis use, indicated by THC-positive urine tests in 10.6% of participants, initially appeared linked to lower brain activation in working memory and motor tasks. However, these associations did not remain statistically significant after adjusting for covariates such as education and race. Despite this, behavioral performance on tasks requiring working memory showed noticeable declines among recent users, suggesting that acute cannabis exposure may temporarily impair cognitive efficiency.
Even more concerning is the observation that heavy lifetime cannabis users exhibited reduced brain activation in working memory tasks even after excluding participants with recent use. This finding underscores the potential for long-term neural adaptations due to chronic exposure to THC, the primary psychoactive component of cannabis. These adaptations may include reductions in cannabinoid receptor density, particularly in regions densely populated with Cannabinoid Receptor 1 (CB1) receptors, such as the dlPFC and anterior insula.
The study also identified sex-specific differences, particularly in motor tasks. Male participants with recent cannabis use showed reduced brain activation, while female participants did not exhibit similar patterns. This suggests potential hormonal or biological factors moderating the effects of cannabis, an area warranting further exploration.
Additionally, correlations between brain activation and measures of education, intelligence, and verbal episodic memory emphasize that cannabis-related neural changes may have broader implications for cognitive and educational outcomes.
Importantly, no significant associations were found between cannabis dependence diagnoses and brain activation outcomes. Instead, the cumulative quantity of cannabis use emerged as a more critical factor influencing neural changes.
Overall, the results demonstrate that heavy cannabis use—whether recent or lifetime—can significantly affect brain function, particularly in areas essential for memory and cognitive control. However, it is important to note that this study does not establish causation but highlights associations warranting further investigation.
Conclusions
To summarize, this study reveals that heavy lifetime cannabis use leads to lasting reductions in brain activation during working memory tasks, while recent use may cause temporary declines in cognitive performance.
These findings underscore the importance of educating individuals about the risks of cannabis use, particularly for tasks requiring focus and decision-making, such as driving or workplace activities. However, public health recommendations must consider that this study identifies correlations rather than causal pathways.
On a broader scale, the results call for increased public awareness and policy interventions to address the cognitive risks associated with heavy cannabis use. Future longitudinal studies are crucial to determining the causality and long-term impact of cannabis on brain health, particularly as its global popularity continues to rise.