["Addiction, EarlyView. ", "\nAbstract\n\nBackground and aims\nAdolescent substance use is a significant public health concern, though the scope of the problem is difficult to ascertain given reliance on self‐reported substance use information. Recent, large cohort studies in adolescents and young adults suggest underreporting of substance use. Analyses here aimed to determine concordance between self‐reported substance use and biochemical verification through hair samples and to estimate prevalence of the three most reported substances used by adolescents.\n\n\nDesign\nObservational cohort longitudinal study design. Liquid chromatography and gas chromatography tandem mass spectrometry (LC or GC/MS–MS) were used to test hair samples for biochemically verified substance use, with results compared with self‐reported substance use. Multi‐step weighting methods estimated prevalence trends of cannabis, alcohol and nicotine use over time, adjusting for discrepancies in sample representation due to recruitment demography, missed visits and hair sample testing.\n\n\nSetting and participants\nData came from the United States nationwide Adolescent Brain Cognitive Development Study (n = 11 868; age 9–10 at baseline, age 15–16 at wave 6). Participants were followed annually, with data here from 2016 to 2024.\n\n\nMeasurements\nHair samples objectively detected at least several days of substance use in a subsample of participants (nsamples = 11 865; n = 6133 unique participants). Participants self‐reported past 3‐month substance use. Sociodemographic, individual and environmental‐level factors were included in inverse propensity weights to estimate prevalence rates of cannabis, alcohol and nicotine use in teens.\n\n\nFindings\nConcordance between self‐report and toxicological data improved with age (for cannabis, ages 11–12 = <1%; ages 15–16 = 45%). Weighted estimates of biochemically verified substance use indicated 7.1% [95% confidence interval (CI) = 6.0–8.3] of 15–16 year olds engaged in biochemically detected cannabis use, 0.2% (95% CI = 0.1–0.4) used alcohol and 4.7% (95% CI = 3.7–6.0) used nicotine.\n\n\nConclusions\nIn United States youth, the concordance between self‐reported substance use patterns and biochemical verification improves with age. Biochemical verification reflects substantive cannabis and nicotine use by United States youth aged 15–16, supporting combining toxicological and self‐report data to improve identification of substance use in youth when possible.\n\n"]