Something is not nothing: Hair-tested substance use and cognitive functions in a large community sample of young adults

Abstract Background Substance use has consistently been linked with cognitive impairments. However, most previous studies have focused on highly selective samples of individuals with chronic substance use disorders and have typically relied solely on self-reports. The associations between recreational use patterns of single or multiple substances and cognitive functioning in representative samples remain unclear. Methods We measured over 100 substances and their metabolites over the past 3 months in 850 young adults (48.6% female, M age = 24.4) from a community-based cohort, using quantitative hair analysis. We assessed sustained attention, working memory, declarative memory, and a total cognitive performance index using the Cambridge Neuropsychological Test Automated Battery. We regressed cognition on hair substance concentrations, adjusting for sex, household socioeconomic status, migration background, education, gaming experience, and self-reported daily tobacco and alcohol use. Results In their hair samples, 386 (45.5%) participants tested positive for at least one psychotropic substance other than alcohol and nicotine. Higher hair concentrations of Δ9-tetrahydrocannabinol (Cohen’s d = 0.40) and codeine ( d = 0.22) were associated with lower sustained attention; higher concentrations of ketamine ( d = 0.59) with worse declarative memory. Higher hair concentrations of cocaine and a higher polysubstance use severity index (PSUSI) were associated with both reduced attention (cocaine: d = 0.21; PSUSI: d = 0.30) and declarative memory (cocaine: d = 0.20; PSUSI: d = 0.29). Conclusions In this community sample of young adults, substance use was highly prevalent and associated with reduced cognitive performance, with small-to-moderate effect sizes. Cognitive consequences of recreational substance use may have been previously underestimated.