An analysis of more than 26,000 middle-aged and older adults has revealed unexpected results about weed and brain health, challenging long-held assumptions about its effects on cognitive function.
Researchers at the University of Colorado Anschutz Medical Campus examined data from 26,362 adults between ages 40 and 77, with an average age of 55, to investigate how weed use relates to brain structure and mental performance. The study findings published suggest that ca**abis users in this age group generally showed larger brain volumes in several key regions and performed better on cognitive tests compared to non-users.
“More older adults are using ca**abis. It’s more widely available and is being used for different reasons than in younger folks, such as for sleep and chronic pain. Plus, people are living longer. We have to be asking, ‘What are the long-term effects of ca**abis use as we continue to age?'” said Anika Guha, PhD, a clinical psychologist at CU Anschutz and lead author of the study.
The research team focused on brain regions with high concentrations of CB1 receptors, the primary target of THC, ca**abis’s main psychoactive component. These areas include the hippocampus, which plays a central role in memory formation and is closely linked to dementia, as well as the caudate, putamen, and amygdala.
The results showed that lifetime weed use was positively associated with larger volumes in these brain regions. Users also demonstrated better performance on tests measuring learning ability, processing speed, and short-term memory. Even individuals who reported using weed only during adolescence showed larger regional brain volumes and better cognitive performance than those who never used the drug.
“The big-picture, overall finding was that greater lifetime ca**abis use among middle aged and older adults was generally associated with larger brain volumes and better cognitive function,” Guha explained.
The findings proved surprising even to the researchers themselves, given decades of research suggesting ca**abis harms cognitive function.
“Even though preliminary work by our group, and some of our colleagues who have also been focused on older adults, had been seeing these beneficial relationships in older adults using ca**abis, I was a little surprised that every cognitive measure that demonstrated a significant effect showed better performance among ca**abis users. It goes against your default assumptions, because I think a lot of research out there has shown ca**abis is associated with worse cognitive function, at least acutely,” Guha said.
However, the picture is not entirely straightforward. One brain region, the posterior cingulate, showed reduced volume in individuals with higher use, suggesting the d**g’s effects are more complex than a simple positive or negative relationship.
The study also revealed dose-dependent patterns. Moderate users often showed the strongest positive outcomes, though some measures, including right amygdala volume and visual memory, also improved with higher use levels. The research team explored differences between men and women, finding that patterns of use and brain effects varied by sex, though no consistent pattern emerged across all measures.
Researchers drew their data from the UK Biobank, a massive health database containing information from over 500,000 adults, including detailed health histories, cognitive assessments, and brain imaging scans. Participants self-reported their weed use, which was then categorized into no use, moderate use, and high use based on lifetime frequency.
The authors suggest that protective effects in older adults may result from how cannabinoids interact with inflammation, immune function, and the processes that lead to neurodegeneration. This contrasts sharply with research on adolescents and young adults, where ca**abis use has been linked to negative outcomes.
“We’re really interested in thinking about both the benefits and risks and understanding this d**g in the context of mental health, dementia and more. There’s so much more to explore,” Guha noted.
She emphasized that the results should not be interpreted as a blanket endorsement of weed use.
“I think the main takeaway is that the story is nuanced. It’s not a case of ca**abis being all good or all bad. 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 ca**abis.’ But it’s more complicated than that. I think it depends on how people are using and what outcomes you’re looking at. Those are important questions and we’re still figuring it out,” Guha said.
The researchers noted that cognitive benefits likely depend on multiple factors, including patterns of use, types of products consumed, and timing of use across a person’s lifespan. The team is continuing to investigate these questions, with ongoing work examining brain connectivity patterns and the potential impacts of psilocybin on older adults.
