The majority of the studies that exist have focused nearly exclusively on comorbidity of substances and gambling behaviors. In these studies, both past year and lifetime rates of alcohol, nicotine, and drug use disorders were consistently higher in Native Americans and lower in Asians, with Blacks, Hispanics, and Whites in between and varying by rank order across studies, timeframes, and the inclusion of covariates in analyses. The small amount of data on overlap suggested variability in the co-occurrence and comorbidity of addictive behaviors across ethnic groups, including higher comorbidity of some addictions for Asians (e.g., gambling and alcohol) and lower comorbidity for Native Americans (e.g., nicotine and drug) than found in other ethnic groups. Importantly, studies have largely focused on concurrent addictions rather than lifetime comorbidity, making it difficult to examine substitution of addictions, which may represent different addictive phenotypes than do concurrently overlapping addictive behaviors. Taking into account rates of use, addiction, and the temporal pattern of co-occurrence and comorbidity of addictive behaviors across ethnic groups is important for understanding the etiology of addiction and warrants additional research.
