A DNA methylation biomarker detected both tobacco and cannabis smoke exposure in high school students

Increasing proportions of students tested positive for cotinine (5-16%), THC (3-10%), and the epigenetic biomarker (5-7%) from 10th to 12th grade. Self-reported combusted tobacco and cannabis use correlated strongly with all biomarkers. The epigenetic marker did not detect e-cigarette use. Dual tobacco-cannabis users had the greatest cumulative exposure. Willingness to smoke and positive perceptions of smokers predicted biomarker positivity.

Longitudinal study of Iowa 10th graders with a friend or family member who smoked, followed through 12th grade. Blood samples at each timepoint for serum cotinine, THC, and DNA methylation at cg05575921. Self-report data on nicotine, tobacco, cannabis, and e-cigarette use.

Self-reported substance use is unreliable in adolescents. An objective epigenetic biomarker that detects both tobacco and cannabis smoke exposure could improve screening, research accuracy, and clinical care.

As adolescent substance use patterns shift between combusted tobacco, e-cigarettes, and cannabis, biomarkers that distinguish between routes of administration become increasingly valuable for research and clinical screening.

High-risk sample (all had a smoking friend or family member) limits generalizability. Epigenetic marker cannot distinguish between tobacco and cannabis smoke exposure. Blood-based testing is more invasive than saliva-based alternatives. Relatively small sample for biomarker validation.