Heavy cannabis use associated with reduced brain activity during memory tasks
Article Written by Adam Isaac Miller
Read time: 2-3 mins
New research has found that people with a history of heavy cannabis use show significantly reduced brain activity during working memory tasks, with effects that appear to persist even after periods of abstinence.
The study, published in JAMA Network Open, analysed brain imaging data from 1,003 young adults to examine how both recent cannabis use and lifetime history of heavy use affect brain function across multiple cognitive domains.
In a comprehensive investigation using functional magnetic resonance imaging (fMRI), researchers from the University of Colorado found that heavy lifetime cannabis users (those with more than 1,000 lifetime uses) showed lower activation during working memory tasks compared to non-users. This effect remained significant even after removing participants with recent cannabis use from the analysis.
Dr. Joshua L. Gowin, the study's lead author, explained: "What makes these findings particularly significant is that the reduced brain activation persisted even after controlling for recent use. This suggests these effects may be long-lasting rather than just temporary consequences of recent cannabis exposure."
The research comes at an important time as more countries and states move towards cannabis legalisation. Recent data shows increasing cannabis potency in products and rising rates of cannabis use disorder, making understanding its long-term effects on brain function increasingly important for public health policy.
Key findings from the study revealed:
Heavy lifetime cannabis users showed significantly lower brain activation during working memory tasks compared to non-users
The effect was most pronounced in brain regions with high concentrations of cannabinoid receptors, including the anterior insula, medial prefrontal cortex, and dorsolateral prefrontal cortex
Recent cannabis use was associated with poorer performance on memory and motor tasks
The relationship between cannabis use and reduced brain activation remained significant even after controlling for factors like education, income, alcohol use, and nicotine use
Dr. Nora D. Volkow, Director of the National Institute on Drug Abuse and co-author of the study, emphasised the public health implications: "As cannabis becomes increasingly legal and accessible worldwide, understanding its long-term effects on brain function becomes crucial for developing evidence-based policies and educational initiatives."
Biological mechanisms explained
The researchers identified several neurobiological mechanisms that might explain their findings. Previous studies have shown that the brain regions most affected by heavy cannabis use have high densities of CB1 receptors, which are the primary targets of THC, the main psychoactive component in cannabis.
"The dorsolateral prefrontal cortex, dorsomedial prefrontal cortex, and anterior insula are critically involved in working memory and other executive functions," noted Dr. Jarrod M. Ellingson, another study author. "The reduced activation we observed in these areas might help explain why heavy cannabis users often report difficulties with memory and concentration."
Animal studies have demonstrated that chronic THC exposure reduces the density and sensitivity of these receptors, suggesting a biological pathway for the observed changes in human brain function.
Implications for cannabis users
The findings have immediate practical implications for cannabis users. The association between recent use and decreased working memory performance suggests that abstaining from cannabis before cognitively demanding situations could help with performance.
However, the researchers noted that for very heavy users, some effects might persist beyond the period of acute intoxication. "Studies suggest that residual cognitive effects of cannabis may remain for 2 to 4 weeks after abstinence," explained Dr. Hollis C. Karoly, study co-author. "Furthermore, in heavy users, abstaining from cannabis may also lead to withdrawal symptoms, which may last for a week or more following cessation and could also affect performance."
The study also found that recent cannabis use was associated with decreased behavioural accuracy in the theory of mind task, which involves understanding others' mental states. The researchers hypothesised that this could contribute to the increased risk of psychosis observed in some cannabis users, as schizophrenia is associated with profound deficits in theory of mind processes.
The researchers acknowledged several limitations of their study, including its cross-sectional nature, which prevents them from drawing definitive conclusions about causality. They also lacked data on cannabis potency, additional cannabis constituents like cannabidiol (CBD), and detailed information about the timing of heavy use.
"While we can't say with certainty that cannabis use causes these changes in brain function, our findings provide compelling evidence of an association that warrants further investigation," Dr. Gowin concluded. "Large, longitudinal studies are needed to establish causality and determine how long these effects might persist."
This research was supported by the National Institute of Mental Health and the National Institute on Drug Abuse, highlighting the growing institutional interest in understanding cannabis's effects on brain function as legalisation expands globally.
Adam has spent a decade working with unregistered medicines, specialising in Cannabinoid Therapeutics, where he has supported the development, implementation and market entry of multiple cannabinoid product portfolios across Australia, New Zealand, Germany and Brazil. Before working in the medical cannabis field, Adam spent nearly ten years building various B2B businesses in education, investment, and medicinal cannabis, progressing through roles in business development, strategy, product development, and project management. As one of the early experts in Australia's emerging cannabis industry, he has consulted for private and listed cannabis producers and ancillary businesses since 2015. Adam founded and served on the board of The Medical Cannabis Council, Australia's first not-for-profit industry body. A graduate of the Royal Melbourne Institute of Technology with a Bachelor of Entrepreneurship, he is a frequent public speaker and publishes a widely read industry newsletter. His expertise has been featured in major news outlets, including the Sydney Morning Herald, The Australian Financial Review, Nine News, Startup Smart, SBS, SkyNews, MJBizDaily and other prominent publications.
Disclaimer: This information is shared with a global readership for educational purposes only and does not constitute medical or business advice. All patient-related information has been de-identified OR fictional to protect privacy. Nothing in this article is intended to promote the use or supply of medical cannabis to members of the public.
