Study finds no long-term cannabis cognitive decline

A social-media post shared on May 22 said a study found no long-term cognitive decline associated with cannabis use, but the post did not name the journal, sample sizes or follow-up period. The underlying research appears to be a February 25, 2026 paper in BMJ Mental Health led by Saba Ishrat of the University of Oxford. In that study, researchers said cannabis use was not linked to longitudinal cognitive decline or dementia risk in older adults. The paper used observational data from the UK Biobank and the U.S. Million Veteran Program, along with genetic analyses, to test whether the relationship held up across different methods. ### Which study was the post referring to? The BMJ Mental Health paper is titled “Cannabis use, cognitive function and dementia risk in older adults: observational and genetic analyses.” The journal published it on February 25, 2026, and the listed authors include Ishrat, Daniel F. Levey, Joel Gelernter, Klaus P. Ebmeier and Anya Topiwala. Oxford Population Health said the study examined whether cannabis use was associated with cognitive performance, cognitive decline over time and dementia risk in later life. (mentalhealth.bmj.com) The university’s summary said the work drew on two large cohorts followed over multiple years and used Mendelian randomisation, a genetic method, to probe whether any observed association was likely to be causal. ### How big were the cohorts, and what did researchers measure? The UK Biobank analysis included up to 18,975 lifetime cannabis users and up to 60,598 non-users, according to the BMJ Mental Health abstract. Researchers compared cross-sectional and longitudinal performance across five cognitive domains. The U.S. Million Veteran Program analysis examined 12,222 participants with cannabis use disorder in relation to incident all-cause dementia using Cox proportional hazards models, the paper said. (ndph.ox.ac.uk) Oxford’s summary said UK Biobank participants who reported ever using cannabis were grouped by lower and higher frequency of use, while MVP participants were identified through electronic health records showing cannabis use disorder. (mentalhealth.bmj.com) ### What did the researchers actually find? At baseline, cannabis users scored modestly better on some tests, including numeric memory and fluid intelligence, the BMJ Mental Health abstract said. But the same abstract said researchers found no significant differences in longitudinal cognitive change. In the veteran cohort, cannabis use disorder was not significantly associated with dementia risk, with a hazard ratio of 1.11 and a 95% confidence interval of 0.97 to 1.26, according to the paper. (mentalhealth.bmj.com) The genetic analyses also found no evidence of a causal relationship between cannabis use and either cognitive performance or dementia risk. ### Did the authors say cannabis improved cognition? (mentalhealth.bmj.com) Saba Ishrat said the slightly better baseline scores among cannabis users “should not be interpreted as cannabis improving cognition.” Oxford’s summary said Ishrat attributed those differences more likely to demographic, educational and socioeconomic differences between users and non-users than to any protective effect from cannabis itself. (mentalhealth.bmj.com) Anya Topiwala, a senior clinical researcher at Oxford Population Health, said the team found no evidence that cannabis use was associated with accelerated cognitive decline or increased dementia risk in older adults across the UK and U.S. cohorts. ### What are the limits of this finding? The BMJ Mental Health paper said its conclusions applied within the limits of the cohorts studied and called for more detailed exposure assessment and longer follow-up. (ndph.ox.ac.uk) The abstract also said safety at higher doses or prolonged use remained uncertain. A separate 2024 study in Brain and Behavior followed 5,162 Danish men from early adulthood to late midlife for a mean of 44 years and likewise reported no significant harmful effects of cannabis use on age-related cognitive decline. (ndph.ox.ac.uk) That study focused on men assessed around age 20 and again around age 64, making it a different population and design from the 2026 older-adult paper. (mentalhealth.bmj.com) ### Where can readers find the full paper? BMJ Mental Health hosts the full article under volume 29, issue 1, with the publication date listed as February 25, 2026. Oxford Population Health also published a university summary the same day naming the UK Biobank and Million Veteran Program as the two main cohorts. (mentalhealth.bmj.com) (pubmed.ncbi.nlm.nih.gov)