Cannabis, long associated with cognitive impairment, may actually have a less detrimental impact on mental functioning than previously thought, according to a new study. Research conducted by the University of Copenhagen has found that men who used cannabis over a span of several decades experienced less cognitive decline as they aged compared to those who never used the substance.
The study, which tracked the cognitive health of over 5,000 Danish men, challenges longstanding beliefs about the negative effects of cannabis on brain function. Spanning 44 years, the research offers a comprehensive look at how cannabis use might influence cognitive performance throughout a lifetime.
Historically, cannabis has been stigmatized as a substance that clouds mental clarity, with policies often classifying it as a drug with little medical benefit and high abuse potential. Despite this, an estimated 9.7% of Danish adults aged 16-44 use cannabis annually, reflecting similar trends across many Western nations. Understanding its long-term effects on cognitive health is crucial for public health policy as cannabis legalization expands worldwide.
The Study: A Longitudinal Look at Cannabis and Cognitive Health
Published in Brain and Behavior, the study followed 5,162 men from their early 20s to their mid-60s, using standardized intelligence tests to measure cognitive abilities at two key points in their lives: during their mandatory military service at around age 20 and again at age 64. The research spanned several decades, tracking participants from the late 1960s to the early 2020s, offering a unique perspective on the long-term impacts of cannabis use.
The results were surprising. Rather than showing accelerated cognitive decline, cannabis users exhibited slightly less mental deterioration over time, with an average difference of 1.3 IQ points compared to non-users. While the difference was modest, it was statistically significant.
No Strong Link Between Frequency or Age of First Use
Among the 39.3% of participants who reported using cannabis at least once, the study explored factors such as the age of first use and frequency of consumption. Contrary to previous studies that suggested early or frequent use could exacerbate cognitive decline, this research found no significant correlation between the age of initiation or frequency of use and cognitive deterioration.
All participants experienced some cognitive decline over the study period—about 6.2 IQ points on average—yet cannabis users declined by an average of 5.3 points, compared to 6.8 points for non-users. This difference remained statistically significant even after adjusting for variables like education level, alcohol and tobacco use, psychiatric history, and other drug consumption.
The intelligence test used in the study, Børge Prien’s Prøve, assessed various cognitive abilities, including reasoning, verbal skills, and numerical problem-solving, allowing researchers to directly measure changes in mental performance.
Factors Beyond Cannabis Use
The study also examined whether other factors, such as the timing of cannabis use or frequency, played a role in cognitive decline. Surprisingly, neither early use (before age 18) nor frequent use (at least twice per week) showed any significant impact on the cognitive trajectories of users.
Interestingly, cannabis users tended to have higher baseline intelligence and educational levels. They were also more likely to consume tobacco and alcohol, suggesting that the relationship between cannabis and cognitive function is complex and influenced by a range of lifestyle factors.
Limitations and Caveats
Despite these findings, researchers were cautious in their conclusions. The difference in cognitive decline between cannabis users and non-users, while statistically significant, was modest—about 1.3 IQ points, or 7% of a standard deviation. This change may not be substantial enough to have a meaningful impact in real-world terms.
Additionally, the study had several limitations. It focused exclusively on men and had a relatively low participation rate (14.3%) for the follow-up testing. The participants who completed the study were generally more educated and had higher baseline intelligence than those who did not, potentially making the results less representative of the broader population.
Most notably, the study found that 92.4% of cannabis users had not consumed marijuana in the year before the follow-up test, meaning the results may reflect the long-term effects of past cannabis use rather than ongoing use into older age.
Possible Explanations and Future Research
What might explain the unexpected findings? Recent animal studies suggest that certain cannabinoids could have positive cognitive effects. For example, research in rats has shown that stimulating cannabinoid receptors can improve memory in older animals, while studies in mice have demonstrated that low doses of THC might restore cognitive function in aging subjects. However, the mechanisms behind these effects, and whether they are applicable to humans, remain unclear.
While this study provides valuable insight into the long-term cognitive effects of cannabis, researchers stress that more studies are needed to fully understand its impact. The study’s findings also do not suggest that cannabis actively protects brain function, but rather indicate that moderate use earlier in life may not significantly accelerate cognitive aging.
As cannabis policy continues to evolve around the world, this research contributes essential data to the ongoing debate about the substance’s potential risks and benefits. However, the study’s focus on men means the results may not be directly applicable to women, warranting further research to explore potential gender differences.
Related topics:
Mental Health Challenges in Multiple Sclerosis: An Overlooked Aspect of the Disease
Korea Partners with World Bank to Tackle Global Mental Health Challenges
Social Media’s Mental Health Toll on Kids Sparks Legal Action and Parental Concern
