Long-Term Study Finds Cannabis Use Does Not Accelerate Cognitive Decline
A groundbreaking study spanning 44 years and involving over 5,000 men has found no significant harmful effects of cannabis use on age-related cognitive decline.
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On the contrary, researchers observed that participants with a history of cannabis use experienced slightly less cognitive decline compared to non-users, challenging longstanding stereotypes about cannabis and mental function.
Key Findings
Cognitive Decline Rates
Across all participants, the mean cognitive decline from early adulthood to midlife was 6.2 IQ points.
Cannabis users showed 1.3 fewer IQ points of decline than non-users, even when adjusting for confounding factors such as education and baseline IQ.
Frequent and Early Cannabis Use
Long-term and frequent cannabis use did not significantly contribute to cognitive decline.
The age of cannabis initiation also had no measurable impact on cognitive decline rates.
Health and Behavior Factors
Cannabis users tended to have higher baseline IQ and education levels. They also smoked more tobacco and drank more alcohol, which could confound the results.
Alignment with Animal Research
Findings align with previous animal studies, which suggest cannabinoids may positively influence cognitive function and memory under certain conditions.
Reactions and Context
Study Authors’ Perspective
The University of Copenhagen research team emphasized that while the observed differences were modest, the findings contribute to growing evidence that cannabis use does not accelerate cognitive aging. They noted that other factors, such as personality traits or lifestyle, may explain why cannabis users experienced less decline.
NORML's Commentary
Paul Armentano, deputy director of NORML, highlighted the study’s significance in dispelling myths about cannabis users. He criticized the lack of mainstream attention to such research, noting that these results contradict widespread stereotypes.
Supportive Evidence from Other Studies
Medical Cannabis and Cognitive Function
JAMA Network Open (2024): Found no significant cognitive impairments in adults using cannabis for chronic conditions like pain, anxiety, or poor sleep.
Anti-Aging Effects: Research on low-dose THC demonstrated restored cognitive abilities and increased synaptic density in aged mice, hinting at therapeutic potential.
Cognitive Decline and Recreational Use
A study published in Current Alzheimer Research reported that cannabis users experienced less subjective cognitive decline (SCD)—a potential precursor to dementia—compared to non-users.
Psychiatric and Neurological Concerns
Adolescent Use: Longitudinal studies found no direct link between cannabis use and early onset of psychosis in at-risk youth. In some cases, cannabis use correlated with improved cognitive and social functioning.
Brain Structure: Studies have found no evidence that cannabis use alters brain structure, contradicting earlier concerns about long-term brain damage.
Implications for Public Policy
This and other recent findings suggest that fears about cannabis causing irreversible cognitive damage may have been overstated. As legalization expands, such evidence could help inform public health campaigns and regulatory frameworks that emphasize science-based approaches over stigma.
However, researchers continue to advocate for more nuanced studies, particularly to understand the role of lifestyle, baseline health, and genetic factors in shaping the long-term effects of cannabis use.
Conclusion
The Danish study adds to a growing body of evidence that cannabis use does not contribute to accelerated cognitive decline and may, under certain conditions, be associated with modest benefits. These findings challenge deeply ingrained societal assumptions, paving the way for a more evidence-based discussion on cannabis reform and its long-term health implications
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