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.
In healthy young adults who use both alcohol and cannabis, the two drugs produce largely separate effects: cannabis primarily alters mood and subjective experience, while alcohol impairs cognitive and psychomotor performance. In a double-blind, placebo-controlled trial with 28 participants aged 19–29, those who received active cannabis (12.5% THC) showed greater increases in tension-anxiety, confusion, euphoria, and sedation compared to placebo, but minimal changes in cognition. Alcohol (target breath alcohol content 80 mg/dL) caused declines in verbal recall, digit-symbol substitution, and fine motor speed, with little effect on mood. Combining the two drugs produced additive effects, not synergistic.