There are a number of environmentally and genetically influenced risk factors that could potentially enhance the development of substance dependence. One set of factors is the presence of co-morbid internalizing (anxiety and depression) and externalizing (antisocial personality/conduct) disorders. One theory of the cause of the increased rates of substance use disorders seen in some Native American tribes is that memories of historical and current trauma, conditions on reservations, prejudice, economic hardship, etc. may lead to increased rates of anxiety and depression leading to increased substance use and dependence, a hypothesis called “self medication”. However, a number of investigators have studied the co-morbidity of substance use and dependence with internalizing disorders and do not find increased rates of internalizing disorders [see 27].
