Can cannabis affect memory? Largest study yet investigates

Heavy cannabis use could negatively impact certain types of memory, largest study of its kind to date has found. Image credit: Valeria Mongelli/Bloomberg/Getty Images.

Cannabis use has increased significantly around the world.
Past research shows that regular cannabis use can increase a person’s risk for several health concerns, including risk factors for dementia.
Scientists from the University of Colorado Anschutz Medical Campus have found that heavy cannabis use may negatively impact a person’s working memory.

Recent research shows the use of cannabis has grown significantly around the world, from about 180.6 million people in 2011 to 219 million in 2021.

Much of this growth has been spurred on by recent moves to legalize the use of cannabis in many countries, including the United States, Canada, Thailand, Spain, South Africa, the Netherlands, and Uruguay.

Past studies show that regular cannabis use can increase a person’s risk for certain health issues such as lung damage, mental health issuesTrusted Source, strokeTrusted Source, and heart attack Trusted Source.

Additionally, previous research shows a potential link between cannabis use and known risk factors for dementia.

Now researchers from the University of Colorado Anschutz Medical Campus report that heavy cannabis use may negatively impact a person’s working memoryTrusted Source, which helps in completing cognitive tasks such as learning and understanding language.

The study was recently published in the journal JAMA Network OpenTrusted Source.

How might cannabis impact cognitive functions?

For this study, researchers analyzed data from more than 1,000 young adults aged 22 to 36 who were categorized as one of the following:

heavy cannabis users — used more than 1,000 times over their lifetime
moderate users 10 to 999 times used during their life
nonusers who used cannabis less than 10 times.

Scientists analyzed the neural responses in the brains of participants captured through magnetic resonance imaging (MRI) as they completed seven different cognitive tasks, including tasks testing motor skills, emotion, reward, and working memory.

“I have had an interest in learning how substances such as cannabis affect brain function since I was a teenager,” Joshua L. Gowin, PhD, assistant professor in the Department of Radiology at the University of Colorado Anschutz Medical Campus and first author of this study, told Medical News Today.

“I was fortunate to have an opportunity to do some of that work with this study. I was not only interested in working memory, but I wanted to see how cannabis affected a range of different brain functions, so we looked at seven tasks,” he added.

63% of lifetime heavy cannabis users had working memory issues

Of the seven cognitive tasks, Gowin said working memory was the only one that showed an effect of cannabis. Researchers found that 63% of lifetime heavy cannabis-using participants and 68% of recent cannabis users showed reduced brain activity during their working memory task.

“We found that brain function related to working memory showed effects of cannabis, where heavy cannabis users had lower brain activation,” Gowin explained.

While the adjustment for potential confounding factors indicated that the link between cannabis use and memory problems was not a strong one, the researchers maintain that the potential connection remains a significant one to take into account.

“The effects were small but reliable, so it won’t turn Einstein into Fred Flintstone, but it could add a few clouds into an otherwise clear sky,” said Gowin.

Heavy cannabis use may also impact attention, decision-making

Additionally, scientists discovered that participants who were heavy cannabis users also had reduced brain activity in certain areas of the brain, including the dorsolateral prefrontal cortex, dorsomedial prefrontal cortex, and anterior insulaTrusted Source, which are not only important for memory, but also other processes such as attention and decision-making.

“We are currently exploring whether controlled administration of THC reduces brain activation relative to a placebo, since the current study did not control for when the participants used cannabis,” Gowin added.

Results match clinical practice observations

MNT spoke with Clifford Segil, DO, neurologist at Providence Saint John’s Health Center in Santa Monica, CA, about this study.

“This study in young adults shows what we see in clinical practice that people that choose to use CBD or THC as either edible or smokeable products have proven memory issues,” Segil, who was not involved in the study, commented.

“This shows that people that were young adults, that had heavy use and recent use, had memory problems. So the expectation is choosing to use cannabis products is going to cause you to have memory loss in the long term and the short term,” he explained.

“There’s two things I’d like to see (as next steps for this research,” Segil continued. “I’d like to see, one, if they could reproduce this with driving tasks, to see if both recent and chronic use decreases people’s ability to drive.“

“And two, I would like to see them do this with a subset of patients that are using medical marijuana, to see if that group of patients that are getting medical marijuana have the same kind of memory cognitive issues. So you can do a risk-benefit ratio for people choosing to use cannabis for medical uses,” he added.

Need for more cautious, informed discussion between doctors and patients

MNT also spoke with Jasdeep S. Hundal, PsyD, ABPP-CN, a board-certified clinical neuropsychologist and director of The Center for Memory & Healthy Aging Hackensack Meridian Jersey Shore University Medical Center in New Jersey, about this study.

“As a neuropsychologist who works with patients at risk for cognitive decline, my first reaction to this study was concern, but not surprise,” Hundal, who was also not involved in the study, said.

“Findings like these should prompt more cautious and informed discussions between doctors and patients, especially those at high risk for Alzheimer’s disease or other memory-related conditions,” he continued. “While cannabis is often perceived as harmless or even beneficial for certain medical conditions, this study underscores potential negative cognitive effects, particularly on working memory and executive function, both of which are crucial for maintaining independence and quality of life.”

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