Internalizing characteristics are thought to involve pathways of risk for alcohol and other substance use disorders partially through the mechanism of negative reinforcement,13 that is, the reduction of unpleasant emotional states through drinking, characterized behaviorally as “self-medication.” At a neurophysiological level, this process is considered central to the second stage of the brain disease model of addiction,14 which Koob and colleagues refer to as withdrawal/negative affect.15 Despite resurgent interest in this topic, the association between internalizing characteristics and the initiation, developmental course, and severity of alcohol and substance use disorders is in need of considerable further investigation. There are several methodological and historic reasons for our relatively rudimentary knowledge. Hussong and colleagues2 note that internalizing traits are more difficult than externalizing characteristics to measure reliably during adolescence (the most common onset period of substance use, including alcohol) and that extended timeframes (such as early childhood to adulthood) are under-studied. Also, a longstanding overrepresentation of males in addiction research may have downplayed the potentially greater risk implications of internalizing characteristics among female substance users,2,16–18 for whom internalizing characteristics are more prevalent.19,20
