The effects of naturalistic cannabis use on cognition and subjective experience in older adults with normal cognitive function

Background: Adults over the age of 65 years are the fastest growing group of cannabis users, but there are few studies of the acute effects of cannabis in this population.

Aims: In the present naturalistic study, participants were invited to smoke their preferred legal cannabis in the lab prior to tests of verbal learning and memory, executive function and information processing, and functional vision and visual attention.

Methods: In this counterbalanced, crossover design, performance after cannabis was compared to a sober condition. Blood levels of delta-9-tetrahydrocannabinol (THC) were measured and correlated with cognition.

Results: Participants aged 65–78 (31 in total; 21 male) with normal cognitive function chose to smoke cannabis with an average THC content of 18.7%. Analysis with linear mixed models found that performance on the trail making test versions A and B was decreased 60 minutes after smoking cannabis, compared to the no cannabis condition. The percentage of words retained in the verbal free recall test was significantly higher in the cannabis condition; this was apparently due to a reversal in performance decrement. Smoked cannabis produced robust subjective drug effects. At 60 and 210 minutes, there were unclear correlations of blood THC and metabolites to cognitive performance.

Conclusions: These results suggest that older adults who use cannabis may show decrements in performance on only some tests of cognition, and marked changes in subjective experience.