Study Examines Recent and Long-Term Cannabis Use on Brain Function in Young Adults

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A recently published study examined the effect of recent and lifetime cannabis use on brain function. The abstract of the study noted the need for more research into the effects of both recent and heavy cannabis on long-term brain function, as cannabis use increases globally. More research is needed in this ara to better inform public health policies, the introduction also noted. The cross-sectional study, “Brain Function Outcomes of Recent and Lifetime Cannabis Use,” was published in JAMA Network Open in January 2025.

In this study, data from 1003 US young adults—ages 26-32 years—was analyzed. The data used was from the Human Connectome Project (HCP), which was collected between 2012 and 2015, to assess lifetime cannabis use, dependence diagnosis, and age at first use. Participants with more than 1000 cannabis uses were considered heavy lifetime users (8.8% of participants in this study), moderate users with 10 to 999 uses (17.8%), and non-users if they had fewer than 10 uses (73.4%). Urine samples were also collected at the time of scanning to determine recent cannabis use. The researchers were able to control for comorbid substance use.

Seven tasks (working memory, reward, emotion, language, motor, relational assessment, and theory of mind) were administered during the functional MRI section to assess brain function.

As noted in the abstract and results sections, highlighted results included:

• Heavy lifetime cannabis use was associated with lower activation on the working memory task
• The anterior insula, medial prefrontal cortex, and dorsolateral prefrontal cortex were regions associated with a history of heavy cannabis use
• Recent cannabis use was associated with lesser performance and brain activation in working memory, the episodic verbal memory task, and the theory of mind task
• None of the tasks were shown to have an association with a diagnosis of cannabis dependence

In this study, heavy cannabis users were more likely to be male, have a lower income, and have a lower level of education than non-users, plus have a positive THC urine screen and dependence diagnosis than moderate or non-users.

Limitations to the study included a lack of control group, suggesting that the results should not be understood as causal. Additionally, the results may not be generalizable to other age groups. Timing of heavy THC exposure was not known, as well as data on what a typical THC dose constituted. Psychiatric comorbidities were also not examined.

Ultimately, a lifetime of heavy cannabis use in young adults was associated with a small to medium effect of lower brain activation related to working memory. “Evidence supported that both recent and heavy lifetime cannabis use were associated with diminished brain activation and cognitive performance during working memory,” the researchers stated in the conclusion. “These findings suggest that large, longitudinal studies are needed to assess the causality of cannabis use toward altering brain function and the duration over which these effects persist.”

Reference

1. Gowin JL.; Ellingson JM.; Karoly HC.; Manza, P.; Ross, M.; Sloan, ME.; Tanabe, JL.; Volkow, ND. Brain Function Outcomes of Recent and Lifetime Cannabis Use. JAMA Netw Open. 2025. DOI: 10.1001/jamanetworkopen.2024.57069