Summary: While recent research has suggested potential neuroprotective benefits for older adults, a new study, the largest brain imaging study of its kind, highlights a significant downside for young adults. Examining over 1,000 participants aged 22 to 36, researchers found that heavy cannabis use (defined as 1,000+ lifetime uses) is linked to reduced brain activity in regions critical for decision-making and attention.
Specifically, 63% of heavy lifetime users and 68% of recent users showed diminished neural response during working memory tasks. These findings suggest that while cannabis effects may vary across a lifespan, frequent use during early adulthood can impair the “mental workspace” needed to retain and manipulate information for everyday problem-solving.
Key Facts
- The Study Scope: This is the largest study to use functional MRI (fMRI) to examine how cannabis specifically impacts the neural networks involved in working memory.
- Working Memory Deficit: Working memory—the ability to hold and use information (like following multi-step directions)—was the only cognitive domain out of seven tested to show a statistically significant decline.
- Brain Activity Reduction: Heavy users showed lower activity in the dorsolateral prefrontal cortex and the anterior insula, hubs responsible for executive control and emotional processing.
- The 1,000-Use Threshold: The most pronounced impairments were observed in “heavy users” who had consumed cannabis more than 1,000 times in their lifetime.
- Reversibility Potential: Preliminary data suggest that abstaining from use before a cognitive task could help improve performance, offering hope for recovery through behavioral changes.
Source: University of Colorado
A new study published today in JAMA Network Open explores the effects of both recent and lifetime cannabis use on brain function during cognitive tasks.
The study, the largest of its kind ever to be completed, examined the effects of cannabis use on over 1,000 young adults aged 22 to 36 using brain imaging technology. The researchers found that 63% of heavy lifetime cannabis users exhibited reduced brain activity during a working memory task, while 68% of recent users also demonstrated a similar impact.
This decline in brain activity was associated with worse performance on working memory – the ability to retain and use information to perform tasks. For example, working memory allows a person to follow instructions they’ve just been given or to mentally visualize and manipulate information, like solving a math problem.
‘Make informed decisions’
“As cannabis use continues to grow globally, studying its effects on human health has become increasingly important. By doing so, we can provide a well-rounded understanding of both the benefits and risks of cannabis use, empowering people to make informed decisions and fully comprehend the potential consequences,” said the study’s first author Joshua Gowin, PhD, assistant professor of radiology at the University of Colorado School of Medicine on the University of Colorado Anschutz Medical Campus.
In the study, heavy users are considered young adults who’ve used cannabis more than 1000 times over their lifetime. Whereas, using 10 to 999 times was considered a moderate user and less than 10 times was considered a nonuser.
The researchers then studied the neural response of participants during a magnetic resonance imaging (MRI) session and gave them seven cognitive tasks to complete. The tasks tested working memory, reward, emotion, language, motor skills – such as tapping a finger to map brain control, relational assessment and theory of mind.
Statistically significant effect on brain function
The researchers found that cannabis had a statistically significant effect on brain function during working memory tasks, meaning the observed impact is very unlikely to be due to random chance. This effect was seen in both recent and lifetime cannabis users. The impact was less significant for the other tasks.
“We applied the highest standards to our research, setting rigorous thresholds for statistical significance across all seven cognitive function tests. To minimize the risk of false positives, we employed false discovery rate (FDR) correction. While some of the other tasks indicated potential cognitive impairment, only the working memory task showed a statistically significant impact,” adds Gowin.
During working memory tasks, the researchers found heavy cannabis use appeared to reduce brain activity in certain areas of the brain (dorsolateral prefrontal cortex, dorsomedial prefrontal cortex and anterior insula). These regions of the brain are involved in important cognitive functions such as decision-making, memory, attention and emotional processing.
However, Gowin mentions their research also suggests that abstaining from using cannabis before doing a cognitive task could help to improve performance. “People need to be aware of their relationship with cannabis since abstaining cold turkey could disrupt their cognition as well. For example, heavy users may need to be more cautious,” Gowin says.
He adds, “There are a lot of questions we still need answers to regarding how cannabis impacts the brain. 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.”
Key Questions Answered:
A: Think of it as your brain’s “sticky note.” It’s the ability to hold a thought while you’re doing something else—like remembering the first half of a sentence while you finish reading the second, or keeping a phone number in your head while you look for a pen.
A: Context is everything. This study focused on young adults (22–36). The brain is still highly plastic in this age range, and frequent use may “blunt” the activity of executive networks. In older adults, the same substance might interact differently with a brain that is already facing age-related decline.
A: The study noted that abstaining before tasks might improve performance, which suggests the impact is functional (how the brain works) rather than purely structural (the brain’s physical shape). More long-term research is needed to see how long it takes for the brain to “re-calibrate” after quitting.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this memory and cannabis research news
Author: Julia Milzer
Source: University of Colorado
Contact: Julia Milzer – University of Colorado
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Brain Function Outcomes of Recent and Lifetime Cannabis Use” by 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 Network Open
DOI:10.1001/jamanetworkopen.2024.57069
Abstract
Brain Function Outcomes of Recent and Lifetime Cannabis Use
Importance
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.
Objective
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.
Design, Setting, and Participants
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.
Exposures
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.
Main Outcomes and Measures
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.
Results
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.
Conclusions and Relevance
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.
