Jan. 28, 2025 – Cannabis use can significantly impact the part of the brain responsible for following instructions, responding during conversations, or remembering a question long enough to answer it. This type of cognitive function is a form of short-term memory called working memory.
That’s according to a new study that observed the impact of cannabis use among young adults ranging in age from 22 to 37 who were considered heavy long-term cannabis users, as well as among young adults who had used cannabis within about the past 10 days.
The study results, from a team led by researchers at the University of Colorado Anschutz Medical Campus, were published Tuesday in JAMA Network Open.
“Our findings highlight the need to educate cannabis users about the consequences of recent and heavy lifetime cannabis use on cognitively demanding working memory tasks,” the authors wrote. “Similarly, the association between heavy use and decreased brain function could motivate regular cannabis users to reduce their cannabis use and could encourage treatment.”
The researchers also analyzed study participants’ performance on six other cognitive functions, but there was no measurable link between cannabis use and participants’ performance. The study also incorporated magnetic resonance imaging (MRI) scans of people’s brains, which linked heavy long-term cannabis use to reduced activity in brain regions called the dorsolateral prefrontal cortex, dorsomedial prefrontal cortex, and anterior insula. Those regions are involved in cognitive functions like decision-making, memory, attention, and emotional processing.
For the study, the researchers used data from 1,206 young adults whose average age was 29 who participated in the Human Connectome Project. The people completed tasks that measured seven brain functions, and they also reported their lifetime cannabis use and provided a urine sample for a toxicology screen at the time of the brain MRI scan. A positive result on the screening typically means a person used cannabis in the past 10 days.
The people in the study were categorized based on both their lifetime use and recent use.
For the recent use portion of the study, 106 people tested positive, including 19 people who were considered non-users because they said they had used cannabis less than 10 times in their lifetime.
For the lifetime use portion of the study, heavy use was considered 1,000 or more lifetime uses, moderate was considered 11 to 999 uses, and non-use was 10 times or less. There were 88 heavy users, 179 moderate users, and 736 non-users.
The link between reduced working memory and lifetime heavy cannabis use persisted when the researchers only looked at data from the heavy lifetime users who did not test positive for recent use.
The researchers also analyzed the data based on whether a person met the diagnostic criteria for cannabis use disorder.
“We observed an absence of an association of a dependence diagnosis with brain function, suggesting that factors associated with diagnosis, such as social and legal consequences, may be unrelated to brain function outcomes attributable to cannabis use,” the study authors wrote. “Thus, the diagnoses of dependence may be less relevant than recent or cumulative exposure to pharmacologically active components of cannabis (eg, THC).”
In a news release, the lead author of the study called for further research.
“There are a lot of questions we still need answers to regarding how cannabis impacts the brain,” said Joshua Gowin, PhD, assistant professor of radiology at the University of Colorado Anschutz Medical Campus. “Large, long-term studies are needed next to understand whether cannabis use directly changes brain function, how long these effects last and the impact on different age groups.”
