The internalizing domain has also been linked to substance problems, although these relationships are less frequently studied, particularly their longitudinal links, and they are often smaller in magnitude than those found for externalizing traits.7 Nevertheless, internalizing conditions such as anxiety and mood disorders are well known to co-occur with substance use disorders at high rates.8,9 For example, persons with internalizing disorders have two to eleven times the odds of having alcohol dependence when compared to subjects without such psychiatric co-morbidity.10 In addition, internalizing disorders are associated with an increased likelihood of relapse after substance treatment,11 and there is some evidence for connections between very early internalizing characteristics and adult substance initiation and/or problems many years later.12
