22/02/2026
https://pmc.ncbi.nlm.nih.gov/articles/PMC11541857/
A 44-year investigation is reshaping the conversation around cannabis and brain health.
Researchers in Denmark followed more than 5,000 men from early adulthood into their mid-60s, comparing intelligence test scores taken at age 20 with follow-up assessments decades later. The study, published in Brain and Behavior, found no evidence that long-term cannabis use speeds up cognitive decline.
In fact, participants who had used cannabis showed a slightly smaller drop in IQ over time—about 1.3 points less on average—than those who had never used it. While the difference is modest, it directly challenges the long-standing assumption that cannabis inevitably erodes mental sharpness with age.
The researchers also looked closely at patterns of use. Surprisingly, neither how often someone used cannabis nor the age at which they began had a measurable impact on their intelligence at 64. However, the study did point to an important factor: “cognitive reserve.” Many cannabis users in the cohort started with slightly higher IQ scores and education levels—both of which are known to help protect against age-related cognitive decline.
Of course, the findings come with limitations. The study included only men and relied partly on self-reported cannabis use. Still, with a follow-up period spanning more than four decades, it stands as one of the most comprehensive longitudinal analyses ever conducted on the subject.
As debates around cannabis policy and public health continue worldwide, this research adds a nuanced layer to the discussion—suggesting that long-term use does not automatically translate into accelerated brain aging.
📚 Source: Christensen, T. W., Mortensen, E. L., & Osler, M. Cannabis use and change in intelligence from age 20 to 64: A 44-year follow-up of 5,162 Danish men. Brain and Behavior.
