From the epidemiological perspective, a major contribution of this study is the demonstration that the course of drug use and problem use is influenced by risk factors at multiple levels, including sociodemographic characteristics, history of childhood abuse, family history of substance use disorders, current health status, use of other substances, and axis I and II psychopathology. Given this complexity, treatment and preventive interventions are likely to be most successful if they intervene on more than one risk factor. An important direction for future research will be the development of comprehensive development models of the etiology and course of drug use disorders, similar to those that already exist for depression (6). These models, by allowing us to understand how risk factors interact with each other over time, may help guide the development of age- or development-specific interventions. For example, prevention and treatment of childhood abuse or close monitoring of individuals with a family history of drug use disorders may be particularly important intervention targets for children and adolescents, whereas treating comorbid psychiatric disorders may be more important in adults. The interventions may also have to be different depending on whether they seek to address drug initiation, transition to problem use, or treatment of drug problems.