Deconstructing the heterogeneity of alcohol use disorder: lifetime comorbid non-alcohol substance use disorder as a distinct behavioral phenotype?

BACKGROUND: Alcohol use disorder (AUD) is an etiologically and clinically heterogeneous condition. Accumulating evidence suggests that persons with lifetime histories of comorbid AUD and non-alcohol substance use disorder (DRUG) constitute an important subgroup of AUD. This study evaluated the distinctiveness of the comorbid AUD/DRUG behavioral phenotype in a community sample with respect to risk factors, AUD course features, and outcome variables assessed at age 30. Contrast groups included persons with histories of AUD only, DRUG only, and neither AUD nor DRUG. METHODS: This research utilized a prospective study design with an age-based cohort (n = 732). Participants completed four comprehensive diagnostic evaluations during the high-risk periods of adolescence, emerging adulthood, and young adulthood. RESULTS: The comorbid AUD/DRUG group was distinguished from the AUD only group by risk factors, AUD course features, and outcomes. Group differences in outcomes were also explained by overall substance use disorder (SUD) severity. Persons with AUD/DRUG comorbidity were indistinguishable from those with DRUG only histories with respect to risk factors and outcomes but demonstrated greater overall SUD severity. Persons with AUD only were indistinguishable from those with neither AUD nor DRUG histories in risk factor endorsements and were mostly similar in outcomes. CONCLUSIONS: Findings collectively suggest that young adults with histories of AUD only and those with comorbid AUD/DRUG are drawn from dissimilar populations. Similarities between the AUD only group with those absent AUD or DRUG histories are likely related to the former group's developmentally limited AUD course accompanied by relatively few or short-lived alcohol-related problems.