As cannabis legalisation expands and marijuana products become more potent, scientists are racing to understand the drug’s long-term effects. Researchers from the National Institute on Alcohol Abuse and Alcoholism, the University of Colorado School of Medicine and the University of Toronto recently published one of the largest studies ever conducted on how cannabis affects brain function.

Their findings, featured in JAMA Network Open, suggest that heavy cannabis users may experience persistent cognitive deficits, particularly in memory, even after they quit. Lead researcher Joshua Gowin, PhD, an assistant professor of radiology at the University of Colorado School of Medicine, shared, “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.”

Key findings

The research team analyzed brain scans from 1,003 young adults aged 22 to 36. Participants were categorised into three groups based on their lifetime cannabis use:

Heavy users (more than 1,000 times)Moderate users (10-999 times)Non-users (fewer than 10 times)

Heavy users—who made up about 9% of participants—exhibited lower brain activity during memory tasks than those who rarely or never used cannabis. The biggest differences appeared in brain regions responsible for attention, decision-making and short-term information storage.

Research uncovers cannabis impact on brain connectivity in individuals at risk for psychosis.(Unsplash)

Using data from the Human Connectome Project, researchers examined participants’ brain function using fMRI scans while they performed various cognitive tasks. Heavy cannabis users consistently showed reduced brain activation during memory-related challenges, suggesting a lasting impact on cognitive processing.

However, other brain functions—such as emotion recognition, logical thinking, and understanding social cues—were not significantly affected. Interestingly, the study also highlighted a gender difference: men exhibited more pronounced movement-related brain activity changes under the influence of cannabis than women, hinting at potential sex-based differences in how marijuana affects the brain.

People who had recently used cannabis (confirmed through drug testing) performed worse on memory and movement tasks, reinforcing the idea that cannabis impairs cognition in the short term. However, even those who had stopped using the drug long ago still showed lasting memory deficits.

Gowin advised, “For anyone who uses cannabis regularly, the research suggests it might be helpful to take breaks before tackling mentally demanding tasks.” However, he also cautioned that abruptly quitting cannabis could temporarily disrupt cognitive function, meaning heavy users should be mindful of their approach to cessation.

Why does memory matter?

Working memory acts as a mental sticky note—it helps you remember a phone number long enough to dial it or follow directions without constantly checking your GPS. This type of memory is crucial for everyday tasks, from holding conversations to problem-solving.

Limitations and what this means for cannabis users

This was a cross-sectional study, meaning it cannot definitively prove causation. Additionally, it focused only on young adults and did not account for differences in cannabis potency or consumption methods.

While the study doesn’t prove that cannabis causes long-term cognitive impairment, it raises important questions about how the drug interacts with brain function over time. The findings suggest that heavy users may need to be cautious about their consumption, especially if they rely on sharp memory for work or academic performance.

Central government has given legal status to the cultivation of cannabis in some districts of Rajasthan, Madhya Pradesh and Uttar Pradesh.(AFP)

With cannabis use becoming more mainstream, understanding both its benefits and risks is essential. Whether you’re a casual user or a longtime consumer, this research offers valuable insights into how marijuana might shape cognitive health in the long run.

Cannabis may be legal in more places than ever but that does not mean it is without risks. While occasional use may not have significant long-term effects, heavy and prolonged cannabis consumption could leave a lasting imprint on memory. As research continues, it’s clear that the conversation around marijuana’s impact on cognitive health is far from over.

Study reference

Title: Brain Function Outcomes of Recent and Lifetime Cannabis Use

Published in: JAMA Network Open, January 28, 2025

Research Institutions: University of Colorado, National Institute on Alcohol Abuse and Alcoholism, National Institute on Drug Abuse.

Disclaimer: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.