Objectives Studies of the neurocognitive impairments resulting from cannabis use have primarily depended on self-reports to classify heavy versus light cannabis use. Several factors such as body mass and individual differences in tetrahydro Cannabinol (THC) metabolism can lead to a large range of circulating levels of THC among persons who report similar cannabis use. This study examined decision-making and attention as a function of urine levels of THC in a sample of adolescents who reported similar frequency of cannabis use.

Methods Adolescents who reported cannabis use at least 4 days per week were assigned to 1 of the 2 groups based on a median split of THC/creatinine ratios on the day of cognitive testing (high THC and low THC). Cognitive testing included a decision-making task and a test of sustained attention.

Results The high THC group made significantly more disadvantageous choices on the decision-making task and also performed less accurately on a task of sustained attention compared with the low THC group.

Conclusions These results suggest that among adolescent cannabis users who are homogenous in their reported frequency of cannabis use, heterogeneity in urine levels of THC is associated with differences in cognitive impairment. Examining the levels of THC metabolites in the urine may uncover differences in cannabis users that may be masked or minimized if users with large variability in their urinary levels of THC are pooled into the same group based on self-reports of cannabis use.