Contribution of alcohol and drug co-use to substance use problems: Data from a nationally-representative sample of US adults who have never been to treatment

Aims: Combined use of alcohol with drugs elevates risk for problems including injury and driving while intoxicated. We assessed contributions of heavy drinking (5+ drinks for men/4+ for women), drug use (cannabis and other drugs) and simultaneous co-use to DSM-5 alcohol use disorder (AUD) and drug abuse (DA). We expected co-use to increase risk for AUD and DA. Methods: Using population-weighted data from adults in the 2014-2015 National Alcohol Survey who had never been to treatment (N = 3386 drinkers, 50% male, 13% Hispanic, 11% Black, mean age 45 years; N = 439 drug users, 56% male, 20% Hispanic, 15% Black, mean age 36), we tested hypotheses using logistic regression adjusting for demographics, family history of alcohol problems and impulsivity. Results: Ten percent of drinkers and 26% of drug users met criteria for mild AUD; <1% of drinkers and 4% of drug users met criteria for DA. Heavy drinking significantly increased risk for AUD, as did monthly or weekly use of cannabis. When simultaneous co-use was added, increased risk associated with cannabis use was reduced to non-significance. Weekly cannabis use, weekly use of other drugs and simultaneous drug and alcohol co-use were associated with significantly elevated risk of DA. In bivariate analyses, simultaneous co-use was associated with significantly greater endorsement of each of the separate AUD and DA symptom domains, including alcohol craving, tolerance and withdrawal, as well as drug and alcohol social and physical health problems. Conclusion: Healthcare providers should screen for simultaneous co-use of alcohol and drugs to help identify patients who may benefit from substance abuse treatment.