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Frequent Cannabis Use Linked to Reduced Brain Activity in Memory


The results of this study indicate that both recent and frequent and prolonged use of cannabis over the lifetime are linked to reduced brain activity and performance on tasks that require working memory. This means that people who use cannabis frequently may have more difficulty retaining and processing temporary information, which is essential for everyday activities such as following instructions or solving problems.


As more states and countries allow the production and sale of cannabis for medicinal and recreational purposes, there has been an increase in the potency of cannabis-based products, the frequency of use, and cases of dependence.


In addition, increased accessibility to cannabis has been associated with an increase in traffic accidents related to its use.


Frequent use of the substance can also lead to health problems, such as cannabinoid hyperemesis syndrome (a disorder characterized by intense episodes of vomiting) and cardiovascular disease.


However, even with these negative effects, many people still believe that cannabis does not pose health risks. Therefore, it is essential to deepen knowledge about its short- and long-term impacts to support public health policies.

Research suggests that, in the short term, cannabis can impair cognitive functions, such as verbal memory. However, these effects may disappear after 72 hours of not using it.


Since the main active compound in cannabis, THC, interferes with the brain's natural cannabinoid system, scientists believe that this may affect areas of the brain that have many receptors for this substance.


Studies suggest that adolescent cannabis users may have a thinner prefrontal cortex, a region of the brain that is essential for planning and impulse control.


Several studies have examined how cannabis affects brain function. For example, research shows that frequent users show greater activation of certain brain regions when exposed to cannabis-related stimuli, which may indicate a strong craving for the substance.


In addition, individuals who began using cannabis in adolescence may have changes in the connectivity between different regions of the brain.

Frequent use is also associated with reduced brain activity in areas involved in memory, emotion control, reward processing and social interaction. However, most of these studies have involved fewer than 30 participants, which limits the strength of the conclusions.


To further investigate this issue, researchers at the University of Colorado Anschutz Medical Campus, USA, used data from the Human Connectome Project (HCP), a large database of information on brain structure and function.


The study analyzed the relationship between cannabis use and brain activation in different cognitive tasks, considering both lifetime history of use and recent use.


The HCP also allowed factors such as age, socioeconomic status and use of other substances, such as alcohol and nicotine, to be taken into account, ensuring that the results were truly attributed to cannabis.

The study involved more than 1,000 young adults, with an average age of 28.7 years. Participants were divided into three groups: heavy users (more than 1,000 lifetime uses), moderate users (between 10 and 999 uses) and non-users (less than 10 uses).


During the study, functional magnetic resonance imaging scans assessed brain activation while participants performed different tasks, such as tests of memory, language, decision-making and motor control.


The results showed that people with a history of heavy cannabis use had lower brain activation during a working memory task. The areas most affected included the medial prefrontal cortex, the dorsolateral prefrontal cortex and the anterior insula, all regions essential for strategic thinking and decision-making.

Lifetime history of cannabis use and activation during the working memory task. A) Brain images representing regions and effect size. Each of the 4 regions in the working memory task summary were examined separately as a post hoc analysis to determine which regions were associated with cannabis history. The brain image represents the effect size of the comparison between heavy users and non-users for each of the 4 regions. B) Bar graph of the models. The models included lifetime history as an independent variable and adjusted for recent cannabis use (i.e., positive urine screen), age, sex, education, income, alcohol use, and nicotine use. dlPFC indicates the dorsolateral prefrontal cortex and dmPFC indicates the dorsomedial prefrontal cortex.


Recent use was also associated with lower activation in memory and motor control tasks, but these differences were not statistically significant. No other brain functions analyzed showed a clear relationship with substance use.


In summary, the study suggests that heavy and prolonged cannabis use may be linked to deficits in brain activation in areas responsible for working memory. These effects may be long-lasting and impact cognition in young adults, even if they are otherwise healthy.


These findings reinforce the importance of continuing to investigate the impacts of frequent cannabis use on the brain and highlighting potential risks to cognitive functioning.



READ MORE:


Brain Function Outcomes of Recent and Lifetime Cannabis Use

Joshua L. Gowin, Jarrod M. Ellingson,  Hollis C. Karoly, Peter Manza, J. Megan Ross, Matthew E. Sloan, Jody L. Tanabe, and Nora D. Volkow

JAMA Netw Open. 2025;8(1):e2457069. doi:10.1001/jamanetworkopen.2024.57069


Abstract:


Cannabis use has increased globally, but its effects on brain function are not fully known, highlighting the need to better determine recent and long-term brain activation outcomes of cannabis use. To examine the association of lifetime history of heavy cannabis use and recent cannabis use with brain activation across a range of brain functions in a large sample of young adults in the US. This cross-sectional study used data (2017 release) from the Human Connectome Project (collected between August 2012 and 2015). Young adults (aged 22-36 years) with magnetic resonance imaging (MRI), urine toxicology, and cannabis use data were included in the analysis. Data were analyzed from January 31 to July 30, 2024. History of heavy cannabis use was assessed using the Semi-Structured Assessment for the Genetics of Alcoholism, with variables for lifetime history and diagnosis of cannabis dependence. Individuals were grouped as heavy lifetime cannabis users if they had greater than 1000 uses, as moderate users if they had 10 to 999 uses, and as nonusers if they had fewer than 10 uses. Participants provided urine samples on the day of scanning to assess recent use. Diagnosis of cannabis dependence (per Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria) was also included. Brain activation was assessed during each of the 7 tasks administered during the functional MRI session (working memory, reward, emotion, language, motor, relational assessment, and theory of mind). Mean activation from regions associated with the primary contrast for each task was used. The primary analysis was a linear mixed-effects regression model (one model per task) examining the association of lifetime cannabis and recent cannabis use on the mean brain activation value. The sample comprised 1003 adults (mean [SD] age, 28.7 [3.7] years; 470 men [46.9%] and 533 women [53.1%]). A total of 63 participants were Asian (6.3%), 137 were Black (13.7%), and 762 were White (76.0%). For lifetime history criteria, 88 participants (8.8%) were classified as heavy cannabis users, 179 (17.8%) as moderate users, and 736 (73.4%) as nonusers. Heavy lifetime use (Cohen d = −0.28 [95% CI, −0.50 to −0.06]; false discovery rate corrected P = .02) was associated with lower activation on the working memory task. Regions associated with a history of heavy use included the anterior insula, medial prefrontal cortex, and dorsolateral prefrontal cortex. Recent cannabis use was associated with poorer performance and lower brain activation in the working memory and motor tasks, but the associations between recent use and brain activation did not survive false discovery rate correction. No other tasks were associated with lifetime history of heavy use, recent use, or dependence diagnosis. In this study of young adults, lifetime history of heavy cannabis use was associated with lower brain activation during a working memory task. These findings identify negative outcomes associated with heavy lifetime cannabis use and working memory in healthy young adults that may be long lasting.

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