Cannabis and tobacco co-use is common and could exposure users to higher levels of toxicants. No studies have examined biomarkers of toxicant exposure in co-users of cannabis and cigarettes, compared with cigarette smokers.Adult daily cigarette smokers were recruited from 10 U.S. sites for a study of reduced nicotine cigarettes. In this analysis of baseline data, participants were categorized as either co-users of cannabis and tobacco (co-users; N=167; urine positive for 11-nor-9-carboxy-Δ9-tetrahydrocannnabinol and self-reported cannabis use ≥1x/week), or cigarette smokers (CS; N=911; negative urine and no self-reported cannabis use). Participants who did not meet either definition (N=172) were excluded. Self-reported tobacco and cannabis use and tobacco/combustion-related biomarkers of exposure were compared between groups.Compared to CS, co-users were younger (co-user Mage=38.96, SD=13.01; CS Mage=47.22, SD=12.72; p<.001) and more likely to be male (co-users=67.7%, CS=51.9%, p<.001). There were no group differences in self-reported cigarettes/day, total nicotine equivalents, or breath carbon monoxide, but co-users had greater use of non-cigarette tobacco products. Compared to CS, co-users had higher concentrations of 3-hydroxypropylmercapturic acid, 2-cyanoethylmercapturic acid, S-phenylmercapturic acid, 3-hydroxy-1-methylpropylmercapturic acid (ps<.05) and phenanthrene tetraol (PheT; p<.001). No biomarkers were affected by number of cannabis use days/week or days since last cannabis use during baseline (p's > .05).Co-users had higher concentrations of biomarkers of exposure than CS, but similar number of cigarettes per day and nicotine exposure. Additional studies are needed to determine whether cannabis and/or alternative tobacco products are driving the increased toxicant exposure.Co-users of cannabis and tobacco appear to be exposed to greater levels of harmful chemicals (i.e., volatile organic compounds and polycyclic aromatic hydrocarbons), but similar levels of nicotine as cigarette smokers. It is unclear if the higher levels of toxicant exposure in co-users are due to cannabis use or the increased use of alternative tobacco products compared with cigarette smokers. It is important for studies examining biomarkers of exposure among cigarette smokers to account for cannabis use as it may have a significant impact on outcomes. Additionally, further research is needed examining exposure to harmful chemicals among cannabis users.
