Cannabis use has risen significantly around the world in recent years, driven by growing social acceptance, legalization efforts, and the widespread belief that it poses relatively little harm.
A recent study, however, is drawing attention to the impact cannabis may have on brain function.
The issue has returned to the spotlight after President Donald Trump shifted cannabis from Schedule I to Schedule III, a move intended to reduce barriers to medical research. The decision has also reignited discussions about the possible long-term health effects associated with the drug.
“Because a lot of people want to see it, the reclassification, because it leads to tremendous amounts of research that can’t be done unless you reclassify,” Trump said, per ABC. “So we are looking at that very strongly.”
That development does not mean cannabis is free of potential risks.
The study, published in JAMA Network Open, explored the relationship between cannabis use and changes in brain activity. Researchers examined 1,000 adults between the ages of 22 and 36 who had cannabis use disorder, utilizing advanced brain imaging techniques. The findings showed that both long-term users and individuals who had used cannabis recently displayed lower brain activity while performing a working memory task. Working memory refers to a person’s ability to process and manipulate information and plays a role in numerous cognitive functions, including reasoning, verbal understanding, and mathematical performance. Joshua Gowin, PhD, the lead author of the study, explained, “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.”
Researchers also found that cannabis use may negatively affect communication among important brain networks responsible for daydreaming, decision-making, concentration, memory, and emotional regulation.
“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,” Gowin added.
Many cannabis users believe that CBD (cannabidiol)—a compound found in cannabis that does not produce a high—can offset the adverse effects of THC, the substance responsible for the intoxicating sensation. However, the study indicates that this may not always be true. In some cases, CBD may actually intensify those effects.
Dr. Daniel Myran, a researcher at the Ottawa Hospital Research Institute and a family physician, also discussed the risk of psychosis among individuals who use cannabis.
“I think that people remain unaware of this connection between cannabis use and potential risk of chronic psychotic disorders,” he said per CBC.
He further warned that males between the ages of 14 and 24 face a risk of ‘developing schizophrenia’ exceeding ‘40 per cent within three years’ if they are treated in the emergency room for cannabis-induced psychosis.
Dr. Myran has spent years examining the relationship between cannabis use and psychosis. He co-authored a 2023 study that identified a 220% rise in Ontario emergency room visits related to cannabis-induced psychosis between 2014 and 2021. He also led research showing that approximately 27.5% of individuals who visited the emergency room due to cannabis use were later diagnosed with an anxiety disorder within three years.
One possible explanation is the substantially higher concentration of THC found in many modern cannabis products compared with naturally occurring cannabis plants. Individuals with existing genetic predispositions or underlying mental health vulnerabilities may face greater risks, with either regular use or, in some cases, even a first-time experience potentially acting as a trigger for psychosis.
