Alcohol and Cannabis Use and Co-Use in Relation to Problematic Use and Driving Under the Influence Among US Young Adults.

BACKGROUND: Young adult (YA) alcohol and cannabis co-use may amplify use-related risks. We examined YA co-use in relation to problematic use and driving-under-the-influence (DUI). METHODS: We analyzed 2023 data among 2,953 US YAs (18-34) reporting past-month alcohol-only use (33.4%), cannabis-only (17.9%), or alcohol-cannabis co-use (48.8%). We assessed self-reported: 1) alcohol-only use vs. alcohol-cannabis co-use, alcohol use frequency, and simultaneous use frequency in relation to problematic alcohol use and DUI of alcohol (DUIA); 2) cannabis-only use vs. co-use, cannabis use frequency, and simultaneous use in relation to problematic cannabis use and DUI of cannabis (DUIC); and 3) alcohol, cannabis, and simultaneous use in relation to DUI of alcohol and cannabis (DUIAC), controlling for sociodemographics and state legalization. RESULTS: Co-use and more alcohol use were associated with greater problematic alcohol use (B = 0.38, SE = 0.04; B = 0.02, SE = 0.01) and DUIA (aOR = 1.35, 95%CI = 1.07-1.72; aOR = 1.07, 95%CI = 1.05-1.08). Co-use and less cannabis use were associated with problematic cannabis use (B = 0.12, SE = 0.04; B=-0.01, SE = 0.003), and more cannabis use was associated with DUIC (aOR = 1.04, 95%CI = 1.03-1.05). Simultaneous use was associated with problematic alcohol (B = 0.02, SE = 0.01) and cannabis use (B = 0.03, SE = 0.01), DUIA (aOR = 1.08, 95%CI = 1.06-1.11), DUIC (aOR = 1.05, 95%CI = 1.02-1.07), and DUIAC (aOR = 1.09, 95%CI = 1.05-1.14). CONCLUSIONS: Interventions should consider addressing both substances, particularly co-use, given related risks.