Moderate Cannabis Use Associated with Larger Brain Regions in Middle Age
Scientists from the University of Colorado Anschutz have uncovered surprising evidence suggesting that moderate cannabis use may be linked to larger brain regions associated with memory and cognition in later life. The research, involving 26,000 participants in their 50s, indicates that those who used cannabis sparingly—between one and 100 times in their lifetime—had more substantial brain volumes in key areas compared to non-users.
Study Details and Participant Demographics
The study, published in the Journal of Studies on Alcohol and Drugs, analyzed data from the UK Biobank, a comprehensive database tracking 500,000 British individuals. All participants were interviewed in 2010, prior to the UK's 2018 legalization of medical cannabis for limited conditions. Recreational use remains illegal in the country.
Of the 26,000 participants aged 40 to 77, with an average age of 55, approximately 5,600 reported cannabis use. Researchers categorized 5,300 as moderate users and 633 as high users, defined as consuming the drug more than 100 times over their lifetime. MRI scans and cognitive tests were conducted to assess brain structure and function.
Key Findings on Brain Volume and Cognitive Performance
Dr. Anika Guha, the neuroscientist leading the study, expressed surprise at the results, which hinted at potential unrealized benefits of cannabis. "We did see that for many of our outcome measures, moderation seemed to be best," she noted in a press release.
The research focused on 11 brain regions rich in cannabinoid receptors, including the hippocampus, crucial for memory consolidation, and the amygdala, central to emotional processing. Compared to non-users, moderate cannabis users exhibited larger volumes in eight regions:
- The left and right putamen, involved in speech articulation and emotional processing
- The right caudate, associated with memory
- The left and right hippocampus
- The left amygdala
- The left and right anterior parahippocampal gyrus, linked to encoding new memories
However, this group also showed smaller volumes in the left and right posterior cingulate gyrus, areas related to self-referential thought and spatial navigation.
High cannabis users, in contrast, had brain regions similar in size to non-users or moderate users, with two exceptions: their left and right posterior cingulate gyrus were smaller than in both other groups.
Cognitive Implications and Dementia Risk
Cognitive tests revealed that moderate users generally performed better on memory and cognition assessments. Dr. Guha emphasized that while larger brain regions do not automatically equate to superior function, the correlation with improved cognitive performance is significant.
Previous studies have linked better cognitive performance to a reduced risk of dementia, suggesting that moderate cannabis use might contribute to a higher cognitive reserve—the brain's ability to withstand age-related damage. This finding adds to a growing body of research, including a 2024 paper indicating that marijuana users experience less cognitive decline over time.
Contradictory Evidence and Health Warnings
Despite these potential benefits, the study's authors caution against overinterpretation. Other research, such as a Canadian study from last year, found that individuals hospitalized for cannabis-related issues had a 72% higher risk of developing dementia.
Experts consistently warn about the dangers of cannabis use, particularly before age 25, when the brain is still developing. The drug can impair brain development and increase the likelihood of mental health problems, including psychosis.
Study Limitations and Broader Context
The research has several limitations. It is observational and cannot definitively prove causation—other factors may influence brain size. Data were self-reported, lacking verification of usage frequency or method of consumption. The study also did not account for THC or CBD content, despite significant increases in potency over recent decades.
In the United States, cannabis is the most commonly used federally illegal drug, with an estimated 52.5 million Americans using it annually. Approximately 18 million report daily or near-daily use, reflecting an 18-fold increase since 1992. Currently, 24 states have legalized recreational marijuana, while 40 permit medical use.
Dr. Guha summarized the complexity of the findings: "I think sometimes people have seen my poster on this project or they see the headline and they say, 'Great, I'll just use more cannabis.' But it's more complicated than that. It's a good reminder that these effects involve multiple processes. It's not all good or all bad."
