Cannabis-linked memory issues may persist long after quitting, scientists warn

STUDY FINDS 

Think cannabis effects wear off once you decide to quit for good? Think again. New research suggests that heavy marijuana use could impact your brain’s memory functions long after your last use. This finding comes from one of the largest studies ever conducted on how cannabis affects brain function.

Against a backdrop of increasing cannabis legalization and rising potency of marijuana products, researchers from the National Institute on Alcohol Abuse and Alcoholism, the University of Colorado School of Medicine, and the University of Toronto collaborated to conduct the largest study of its kind examining how both recent and long-term cannabis use affects brain function. Their findings, published in JAMA Network Open, suggest that heavy cannabis use may have lasting impacts on cognitive processing, even after someone stops using the drug.

“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, an assistant professor of radiology at the University of Colorado School of Medicine, in a statement.

The research team looked at brain scans from 1,003 young adults between ages 22 and 36. They found that people who had used cannabis heavily throughout their lives showed less brain activity during memory tasks compared to those who rarely or never used marijuana. This difference was most noticeable in brain regions that help us pay attention, make decisions, and temporarily store information.

Working memory is sort of like a mental sticky note – it’s what helps you remember a phone number just long enough to dial it. We use this type of memory countless times each day, from following a conversation to solving problems or remembering directions.

The researchers split participants into three groups based on their lifetime cannabis use: heavy users (more than 1,000 times), moderate users (10-999 times), and nonusers (fewer than 10 times). Out of everyone studied, about 9% were heavy users, 18% were moderate users, and 73% rarely or never used cannabis. Heavy users were more likely to be male, have lower income and education levels, and show recent cannabis use in drug tests.

“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,” noted Gowin.

Beyond memory tasks, the study also looked at how participants’ brains responded during other mental challenges – things like processing rewards, recognizing emotions, using language, controlling movement, logical thinking, and understanding others’ perspectives. Interestingly, heavy cannabis use didn’t seem to significantly affect these other brain functions.

The team also found that people who had recently used cannabis (detected through drug testing) performed worse on memory and movement tasks. However, these short-term effects weren’t as statistically strong as the long-term impacts on memory…