Heavy Cannabis Use May Impair Brain’s Working Memory, Study Suggests

Heavy cannabis use may negatively impact one’s working memory, according to a new study from researchers in Colorado.

The study, which comes from researchers at the University of Colorado’s Anschutz School of Medicine, was published on Jan. 28 in JAMA Network Open, having since been described as the “largest of its kind” to be completed. It used brain imaging technology to explore the impact of cannabis use on 1,000 young people between the ages of 22 and 36, per a release from the school, before suggesting that heavy cannabis usage may negatively impact one’s working memory, which it describes as the ability to retain and use information in order to perform tasks.

As the research found, 63% of the heavy lifetime cannabis users who participated showed reduced brain activity amid working memory tasks. As for those who tested positive for recent cannabis use, 68% of them demonstrated a “similar impact” in the study.

“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,” assistant professor Joshua Gowin, the study’s first author, said in a statement.

Speaking with CNN, Gowin gave some real-life examples of working memory in action, such as “checking your blind spot” while driving a vehicle. “When you look back in front of you, you need to remember what you saw in the blind spot before you can make a good decision if you want to change lanes or not,” he said.

“When you’re in the middle of a conversation with your boss, you need to remember what they said long enough to respond to it,” Gowin added. “Losing working memory means that retaining that information might require more effort and be more challenging.”

Carol Boyd — the founding director of the Center for the Study of Drugs, Alcohol, Smoking and Health at the University of Michigan in Ann Arbor, who was not involved in the study — told CNN that while the study cannot prove that cannabis use harms the brain, it adds scientific evidence to what many have long believed about the use of marijuana.

“For years, clinicians, family and friends who knew heavy cannabis users understood that their memories were ‘shot’ — there’s even a term for this, ‘stoner,’ as in ‘forgot the grocery list, couldn’t follow a recipe, couldn’t get it together,’” Boyd told CNN.

In the study itself, which used data from the Human Connectome Project, heavy cannabis users were described as young people who have used cannabis more than 1,000 times, while those who used it 10 to 999 times were considered moderate users. Those who used cannabis less than 10 times were described as nonusers.

Participants took part in magnetic resonance imaging (MRI) sessions and were tasked with completing seven cognitive tasks covering memory, reward, emotion, language and motor skills, per researchers. According to the research, working memory tasks were significantly impacted by cannabis use in both recent and lifetime users. Activity in certain areas of the brain was reduced during the working memory tasks.

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Gowin also shared in a news release that avoiding cannabis use before certain cognitive tasks could 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 said. “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.”

As Boyd told CNN, the research cannot determine if a heavy user quitting cannabis can positively impact working memory.

“Can the adolescent who used cannabis more than 1000 times between the ages of 15 and 20 years of age, but stopped using at 20 years, demonstrate improved working memory 10 years later?” she said. “That is my 64-dollar question — where is the hope for the person with a chronic use disorder who wants their memory back?”

Gowin said, per CNN, that there’s “some evidence” that cannabis users recover some of their memory function while they stop smoking, citing previous studies. Still, “when it comes to chronic marijuana use and the brain, it’s an area in which investigation is ongoing.”