Older adults aged 65–78 who smoked their preferred legal cannabis with an average THC content of 18.7% showed decreased performance on the trail making test (versions A and B) 60 minutes after smoking, compared to when they were sober. However, the percentage of words retained in a verbal free recall test was significantly higher after cannabis, apparently due to a reversal in performance decrement. Smoked cannabis produced robust subjective drug effects. Correlations between blood THC levels and cognitive performance at 60 and 210 minutes were unclear. The findings suggest that older adults who use cannabis may show decrements on only some cognitive tests, along with marked changes in subjective experience.
Inhaled cannabis routes (smoking, vaping) produce higher peak blood THC levels, while edible cannabis has a longer duration of action. Few differences between methods were found for cognitive performance, though two studies indicated worse attention after vaping versus edibles or smoking, and one study found worse memory with high-potency flower containing cannabidiol compared to concentrates. One study reported an inverse correlation between blood THC and cognition. Because THC levels are used to detect impairment, detection may be more challenging with edibles.