In a crossover study of 31 cognitively normal adults aged 65-78, smoking cannabis impaired performance on the trail making test but did not broadly affect other cognitive measures, while producing robust subjective drug effects.
Older adults who use cannabis, healthcare providers working with senior patients, and aging researchers.
Trail making impaired but verbal memory retention actually improved after cannabis in adults 65-78
What the researchers found
Trail making test performance (versions A and B) was significantly decreased 60 minutes after smoking cannabis compared to the sober condition. However, verbal free recall word retention was actually higher after cannabis, apparently due to reversal of a performance decrement. Cannabis produced robust subjective effects. Blood THC levels did not clearly correlate with cognitive performance.
Why it matters
Adults over 65 are the fastest-growing group of cannabis users, yet almost no research examines acute effects in this population. This study provides rare data showing that cognitive impacts may be more selective than expected, affecting processing speed and executive function but not necessarily memory.
The numbers in context
31 participants, ages 65-78, 21 male. Average cannabis THC content: 18.7%. Trail making A and B impaired at 60 minutes. Verbal free recall retention was higher under cannabis. Blood THC measured at 60 and 210 minutes with unclear correlations to cognitive performance.
How the study worked
Counterbalanced crossover design with 31 participants aged 65-78 (21 male) with normal cognitive function. Participants smoked their preferred legal cannabis (average 18.7% THC) in the lab, then completed tests of verbal learning and memory, executive function, information processing, and visual attention at 60 and 210 minutes. Blood THC and metabolites were measured.
What this study cannot tell us
Small sample of 31 participants, predominantly male. Naturalistic design means THC dose was not controlled. Participants were existing cannabis users with normal cognition, so results may not apply to naive users or those with cognitive impairment. Short-term acute effects were measured, not chronic use impacts.
How to read the evidence
Controlled crossover design with counterbalancing, but small sample, uncontrolled dose, and experienced users only.
When this study was published
Published in 2025.
The bigger picture
The finding that blood THC levels did not clearly predict cognitive performance in older adults is important. Age-related changes in metabolism, body composition, and brain function may alter how THC affects cognition compared to younger populations, meaning dosing guidelines based on younger adults may not apply.
Questions still open
- Would cognitively impaired older adults show more pronounced effects? Does tolerance play a role in the selective cognitive impact? Are there specific cognitive domains where older adults are more vulnerable to cannabis effects? Would lower-THC products show fewer cognitive effects?
Common questions
Does cannabis impair thinking in older adults?
Why didn't blood THC levels predict cognitive effects?
Read the original research
The effects of naturalistic cannabis use on cognition and subjective experience in older adults with normal cognitive function.
Journal of psychopharmacology (Oxford, England), 2698811251370975
Citation
Di Ciano, P; Le Foll, B; Zhao, S; Byrne, P; Elzohairy, Y; Brubacher, J R; McGrath, M; Brands, B; Chen, S; Wang, W; Kaduri, P; Wickens, C M; Rajji, T K. (2025). The effects of naturalistic cannabis use on cognition and subjective experience in older adults with normal cognitive function.. Journal of psychopharmacology (Oxford, England), 2698811251370975. https://doi.org/10.1177/02698811251370975
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