A new study shows cannabis use can impair how individuals process information and manage tasks

By Talia Gordon Wexler

The acceptance of marijuana in the United States is rapidly increasing. As of June 26, 2025, 40 states, three territories, and the District of Columbia have legalized marijuana for recreational and medical use. This recent escalation of legalization has required researchers to study the risks, standardization, and future implications of cannabis.

For instance: a 2024 study in JAMA explored cannabis use and brain activation, the increase of brain activity when an individual is engaging in a task or thought. This cross-sectional study, a snapshot of a specific population conducted by researchers at the University of Colorado School of Medicine, found that heavy cannabis use in young adults can harm how they manage information needed to perform complex tasks such as decision-making.

These results created commotion from cannabis business owners who believed that the negative description of marijuana, as cited in the study, could potentially threaten the cannabis business and the promotion of their products.

“I was really interested in painting the picture of what was really going on,” said Joshua Gowin, associate professor at the University of Colorado Anschutz and the first author of the JAMA study.

The researchers took data from an existing database where young adults in the age group of 22-36 years old, were assessed for short-term versus long-term effects of cannabis use. Further, the participants performed a range of tasks to help researchers measure brain activation levels.

The results showed that heavy lifetime users of cannabis had lower brain activation only during memory task, an evidence for a decrease in cognitive function. A positive THC test, evidence for recent use, did not show any connection to reduced brain activity, whereas long-term use did, possibly illuminating the need to evaluate use over time rather than sparing use recreationally.

After the study was published, Dr. Gowin and his team received negative feedback from owners of cannabis stores nationwide. “They were frustrated because they thought we were too critical of the potential negative effects of cannabis,” said Dr. Gowin.

Support of both medical and recreational cannabis has increased with the push for legalization over the past 25 years. As cannabis becomes more mainstream, there is also a push to research the larger public health implications of usage, especially among adolescents and their brain development. The debate around cannabis and cognitive function will only continue to grow as more researchers enter this undefined space.

Dr. Gowin and his team’s work demonstrate the need for further research in this area. They call for a longitudinal study to determine not just correlation but causation, meaning that further research must be done to understand why marijuana use over an extended period of time could be linked to decreased brain activation for memory functions.

Beyond the JAMA study, research on the topic of cannabis continues to grow. Novel studies link cannabis with threatened cardiovascular health, pregnancy, and mental health disorders. But to create such studies, there must be standardization of what a researcher means when someone says, “cannabis use,” as there are many methods of engaging with marijuana, such as smoking or ingesting edibles.

“We need guidelines, standardized guidelines for testing and quality products for cannabis,” said Cerina Dubois, postdoctoral fellow at the Johns Hopkins Cannabis Science Laboratory and  first author of a 2021 study on cannabis impaired driving concerns.

Both Dubois’s and Gowin’s studies contribute to the bigger picture of the public health implications of the increase in legalization in the United States. The results of the JAMA study, along with the need for clearer standardization of cannabis, identify the need for research to continue in this field. Dr. Joshua Gowin said his team is currently working on the next steps for more conclusive results on recent use of marijuana. His current work consists of giving participants a placebo or THC and looking at brain imaging an hour later to “better understand the effects of the recent use on brain function.”