Older adults showed selective cognitive effects after smoking cannabis in naturalistic lab study

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.

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.

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 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.

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.