Joshua Gowin, PhD, assistant professor of radiology, and Justin Juvera, senior professional research assistant and MRI manager.
BRAIN DRAIN
CU radiologist leads study on effect of cannabis on brain function
By Julia Milzer
April 2025
CU Anschutz Medical Campus researchers have conducted the largest study of its kind on the effects of recent and lifetime cannabis use on brain function during cognitive tasks.
The study, published in January in JAMA Network Open, is the largest of its kind ever to be completed. Researchers examined the effects of cannabis use on over 1,000 young adults aged 22 to 36 using brain imaging technology. They report that 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.
Joshua Gowin, PhD
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.
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," says the study’s first author Joshua Gowin, PhD, assistant professor of radiology.
In the study, heavy users are considered young adults who’ve used cannabis more than 1,000 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 cognitive tasks to complete, including tasks that tested working memory, reward, emotion, language, motor skills – such as tapping a finger to map brain control, and relational assessment.
IMPACT ON BRAIN
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.”