Danish Study Challenges the Myths: Cannabis and Brain Health
A comprehensive Danish study from 2024 that followed more than 5,000 men over 44 years shows surprising results regarding cannabis’ impact on cognitive function. The research challenges many established assumptions about long-term cannabis use and brain health.
The Study That Turns Old Assumptions Upside Down
For more than four decades, researchers from the University of Copenhagen followed 5,162 Danish men to investigate the relationship between cannabis use and cognitive decline from early adulthood to late midlife. The results, published in the journal Brain and Behavior, run counter to many previous assumptions.
The study is unique in its kind due to its exceptionally long follow-up period – an average of 44 years per participant. This makes it one of the most comprehensive long-term studies in the field to date.
Less Cognitive Decline Among Cannabis Users
The most striking finding of the study is that men who had used cannabis actually showed less cognitive decline compared to those who had never used cannabis. The difference corresponded to 1.3 IQ points less decline among cannabis users over the entire follow-up period.
This result remained consistent even after researchers controlled for lifestyle factors such as education, alcohol consumption, smoking, and the use of other drugs.
No Impact from Age of Onset or Frequency
The researchers also examined whether age at first cannabis use or frequency of use affected cognitive development. The results showed that:
- Neither early onset (before the age of 18) nor later onset had any significant impact on long-term cognitive decline
- Regular use (at least twice per week) was not associated with increased cognitive decline
- No differences in cognitive development were observed between different user groups
Study Methodology
The study was based on results from the military intelligence test that all Danish men undergo at conscription, typically at around 20 years of age. The same test was then administered again at follow-up when the men were on average 64 years old.
This method gave researchers a unique opportunity to measure actual changes in cognitive ability across an entire adult lifespan, rather than comparing different individuals at a single point in time.
Participants also completed extensive questionnaires about their lifetime cannabis use, including:
- When they began using cannabis
- How frequently they used it during different periods
- Which other drugs they may have tried
What Could Explain the Results?
Temporary Effects
Most cannabis users in the study (92.4%) had not used cannabis during the year prior to the follow-up. This may suggest that any negative effects of cannabis on cognition are temporary and fade after a period of abstinence.
Baseline Factors
The cannabis users in the study initially had slightly higher IQs and education levels, which may have influenced the results. Although the researchers controlled for these factors, other unmeasured variables could still play a role.
Potential Protective Effects
Interestingly, the findings are consistent with animal studies showing that cannabinoids may have positive effects on memory and cognitive function in older rats and mice. This opens the possibility that low doses of certain cannabis compounds could have protective effects on the aging brain.
Previous Research Presents a Mixed Picture
The body of research on cannabis and cognitive ability is complex, and previous studies have shown mixed results:
- A New Zealand study from 2012 found that frequent cannabis use was associated with cognitive decline, particularly among those who began using in adolescence
- A U.S. study from 1999, however, found no difference in cognitive decline between heavy users, light users, and non-users
- An Australian study from 2016 reported similar findings – no link between cannabis use and accelerated cognitive decline
The new Danish study differs from many earlier ones due to its exceptionally long follow-up period and large number of participants.
Important Limitations to Keep in Mind
Men Only: The study included only men, and the results cannot necessarily be generalized to women, as the effects of cannabis may differ between sexes.
Self-Reported Data: Information about cannabis use was based on participants’ own reports, which always involves some degree of uncertainty.
Selective Attrition: It is possible that men with extensive cannabis use were less likely to participate in the follow-up.
What Does This Mean in Practice?
The researchers are careful to point out that although the difference between cannabis users and non-users was statistically significant, it was relatively small and may not have any clinical relevance in everyday life.
The results mainly indicate that long-term cannabis use, at least at the levels common in the studied population, does not appear to lead to the dramatic cognitive decline that many have feared.
It is also important to distinguish between long-term effects and acute effects — even if prolonged use does not seem to affect cognitive aging, it is well established that cannabis has short-term effects on memory and cognitive function during intoxication.
Conclusion
The Danish study provides an important contribution to understanding the long-term effects of cannabis on cognitive health. With its 44-year follow-up period and more than 5,000 participants, it adds substantial knowledge to the research field.
The results suggest that concerns that long-term cannabis use would lead to severe cognitive decline may be exaggerated. At the same time, it is important not to overinterpret the findings — the study does not show that cannabis is “good” for the brain, only that the long-term negative impact appears to be smaller than many previously believed.
For individuals considering their cannabis use, the key message is that potential effects appear to be complex and influenced by many factors. As always, moderation and awareness are essential, and younger individuals in particular should be cautious, as the brain continues developing until around age 25.
Sources
Høeg, K. M., Frodegaard, R. L., Grønkjær, M., Osler, M., Mortensen, E. L., Flensborg-Madsen, T., & Okholm, G. T. (2024). Cannabis Use and Age-Related Changes in Cognitive Function From Early Adulthood to Late Midlife in 5162 Danish Men. Brain and Behavior, 14(11), e70136. https://doi.org/10.1002/brb3.70136
Neuroscience News. (2024, december 16). Study Challenges Myths About Cannabis, Brain Health, and IQ. https://neurosciencenews.com/cognitive-decline-cannabis-28252/
