When Substance Use is Underreported: Comparing Self-Reports and Hair Toxicology in an Urban Cohort of Young Adults.

Our study suggests that self-reports underestimate young adults' exposure to illicit substances and non-medical use of prescription drugs. Consequently, estimates of associations between substance use and risk factors or outcomes are likely biased. Combining self-reports with hair tests may be most beneficial in study samples with occasional substance use. Researchers can use specific factors (e.g., detection ratios) to adjust prevalence estimates and correlations based on self-reports.