The recent largest study on the effects of cannabis on the brains of individuals aged 18 to 36 has discovered that the drug can diminish brain function during cognitive tests. These findings aim to provide people with the necessary information to make informed decisions about the advantages and disadvantages of using cannabis.
With the increasing legalization of cannabis production and sales for recreational and medical purposes in various countries and states, there is an ongoing discussion about its harmlessness, particularly for young adults. Adolescence is a crucial stage for brain development, which continues until the mid-to-late 20s.
While there have been some smaller studies examining the impact of cannabis use on brain function in young individuals, a study conducted by researchers at the University of Colorado is the most extensive yet.
“As cannabis use continues to expand globally, it has become increasingly vital to study its effects on human health,” stated Joshua Gowin PhD, the study’s primary author and assistant professor of radiology at the University of Colorado School of Medicine on the University’s Anschutz Medical Campus. “Through this research, we can offer a comprehensive understanding of both the benefits and risks of cannabis use, enabling individuals to make well-informed decisions and comprehend the potential consequences.”
The researchers collected data from 1,003 adults aged 22 to 36, which included MRI scans, urine toxicology, and details on cannabis use. The average age of participants was 28.7 years, with 53.1% being female. The sample primarily consisted of White participants (76%), but also included Asians (6.3%) and Black individuals (13.7%).
To determine recent cannabis use, participants provided a urine sample on the day of their MRI scan, which was tested for the presence of a THC metabolite. Those with a positive result were classified as recent users. Lifetime cannabis use was also evaluated and categorized: heavy users had used 1,000 or more times, moderate users had used between 11 and 1,000 times, and non-users had used less than 10 times. MRIs measured brain activity during seven tasks assessing emotion, reward, motor function, working memory, language, reasoning, and social information processing.
The researchers found that both recent and heavy lifetime cannabis use was linked to a significant reduction in brain activity only during the working memory task.
University of Colorado Anschutz Medical Campus
“We applied rigorous standards to our research, establishing strict thresholds for statistical significance across all seven cognitive function tests,” Gowin explained. “To reduce the risk of false positives, we utilized false discovery rate (FDR) correction. While some tasks indicated potential cognitive impairment, only the working memory task displayed a statistically significant effect.”
Working memory entails the temporary retention of limited information that can be accessed to guide decision-making and behavior. Following directions, recalling a conversation in progress, and following recipe steps are examples of working memory tasks.
The researchers noted that the diminished brain activity observed in heavy cannabis users during the memory task was most pronounced in specific brain regions: the dorsolateral prefrontal cortex, dorsomedial prefrontal cortex, and anterior insula. Each region contributes to crucial brain functions associated with emotion, cognition, and social behavior, often collaborating to process complex tasks and decisions.
The researchers suggested that recent cannabis users may benefit from abstaining before a mentally demanding task to enhance performance. However, for heavy users, abstaining comes with additional considerations.
“The connection we observed between recent use and working memory task activation and performance implies that abstaining from cannabis before cognitively demanding situations is likely to enhance performance,” the researchers mentioned. “The exact duration of this abstinent period is uncertain, but studies indicate that cognitive effects of cannabis may persist for 2 to 4 weeks post-abstinence. Additionally, heavy users may experience withdrawal symptoms upon abstaining, potentially lasting a week or more after cessation and affecting performance.”
The study has its limitations. It was an uncontrolled, cross-sectional study, meaning the relationship between cannabis and brain function cannot be deemed causal. Moreover, as the participants were young adults, the results may not be generalizable to other age groups. The researchers also lacked data on typical THC dose and potency, additional components like cannabidiol (CBD), and the method of cannabis administration.
“Numerous questions remain regarding how cannabis impacts the brain,” Gowin stated. “Extensive, long-term studies are essential to determine whether cannabis directly alters brain function, the duration of these effects, and the impact on various age groups.”
The study was published in the journal JAMA Network Open.
