People who have used cannabis more than 1,000 times show memory problems from cannabis and reduced brain activity during memory tasks, even long after stopping use. The effects were most noticeable in brain regions responsible for working memory.
Our focus on presenting this article is to present employers reasons to continue to drug test for cannabis in your drug testing program.
AURORA, Colo. — 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.
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. [R&A Comment – Do you as an employer want to have employees in your workforce who can’t pay attention, make decisions and temporarily store information?]
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.
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.
For anyone who uses cannabis regularly, the research suggests it might be helpful to take breaks before tackling mentally demanding tasks. [ R&A Comment –You’re your firm afford to pay for these breaks that heavy marijuana users need?] However, Gowin warned that suddenly stopping cannabis use could also affect thinking abilities. “People need to be aware of their relationship with cannabis since abstaining cold turkey could disrupt their cognition as well,” he said. “Heavy users may need to be more cautious.”
Results
Heavy lifetime cannabis users showed significantly lower brain activation during working memory tasks compared to non-users, with a moderate effect size (Cohen’s d = -0.28). This association remained even after excluding participants with recent cannabis use. The effect was most pronounced in brain regions with high densities of cannabinoid receptors. Recent cannabis use was associated with poorer performance on working memory and theory of mind tasks, though these effects didn’t survive the strictest statistical corrections.
Limitations
This research was cross-sectional rather than longitudinal, meaning it can’t definitively prove that cannabis use caused the observed differences in brain function. The study focused on young adults, so findings may not generalize to other age groups. Researchers lacked detailed information about when heavy cannabis use occurred in participants’ lives and couldn’t account for differences in marijuana potency or consumption methods.
Discussion & Takeaways
These findings suggest that heavy cannabis use may have lasting effects on brain function, particularly working memory, even after cessation. This has important implications for public health messaging around marijuana use. The research indicates that users may benefit from periods of abstinence before cognitively demanding tasks, though the optimal duration of such breaks remains unclear.
Funding & Disclosures
This research was supported by the National Institute of Mental Health, National Institute on Drug Abuse, and other NIH institutes through the Human Connectome Project. Several authors reported receiving various research grants, but no significant conflicts of interest were disclosed.
Publication Information
This study, titled “Brain Function Outcomes of Recent and Lifetime Cannabis Use,” was published in JAMA Network Open on January 28, 2025. The research was led by Joshua L. Gowin, PhD, and colleagues from multiple institutions including the University of Colorado, National Institute on Alcohol Abuse and Alcoholism, and National Institute on Drug Abuse.
James P. Randisi, President of Randisi & Associates, Inc., has since 1995 been helping employers protect their clients, workforce and reputation through implementation of employment screening and drug testing programs. Mr. Randisi can be contacted by phone at 410.494.0232 or Email: jim@preemploymentscreen.com or the website at preemploymentscreen.com
