AURORA, Colo. – Frequent marijuana use may have lasting effects on working memory, according to the largest study of its kind, published in JAMA Network Open. Working memory—the ability to retain and use information for tasks like following instructions or solving problems—showed measurable impairment among heavy cannabis users.
Researchers analyzed brain scans from more than 1,000 young adults aged 22 to 36 and found that 63% of heavy lifetime cannabis users showed reduced brain activity during a working memory task. Among recent users, 68% exhibited similar deficits.
“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 in a University of Colorado Anschutz Medical Campus press release.
The study classified heavy users as those who had used cannabis more than 1,000 times. Moderate users had consumed cannabis between 10 and 999 times, while non-users had done so fewer than 10 times.
While Gowin emphasized that rigorous scientific standards were applied to the research, he noted that even larger, long-term studies are needed to determine whether cannabis directly alters brain function, how long these effects last, and how they vary across different age groups.