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Epilogue to Dual Diagnosis Special Issue

The reviews in this issue covered a variety of dual diagnosis topics. Three of the papers reviewed the treatment of patients with severe psychiatric illnesses (bipolar disorder, schizophrenia, posttraumatic stress disorder) and substance use disorders (1,2,3). There are similarities and differences in the literature on the illnesses. However, the number of randomized, controlled trials is modest in each of these dual diagnosis populations. Furthermore, many of the interventions tested did not demonstrate superior efficacy to the control condition. The available literature in bipolar disorder is dominated by pharmacotherapy studies, while most studies in schizophrenia focus on psychosocial interventions. In bipolar disorder, positive results were observed with divalproex for alcohol dependence (4) and citicoline for cocaine dependence (5). In schizophrenia, positive findings are reported with interventions based on cognitive-behavioral approaches and motivational interviewing (2). Many studies in both populations are limited by small sample sizes. The literature in posttraumatic stress disorder and alcohol use disorder has many of the same limitations as with bipolar disorder and schizophrenia, with many studies showing negative results and having small sample sizes. In general, the studies in posttraumatic stress disorder and alcohol use disorder were more likely to demonstrate a reduction in alcohol consumption than in posttraumatic stress disorder symptoms (3). Larger and more definitive trials, as well as new treatment options, are needed in each of these patient populations. The small sample sizes and lack of statistical power are particularly concerning. While dual diagnosis is common, it represents a subsample of people with substance use disorders. Thus, patient enrollment can be challenging. For this reason, multisite clinical trials may be needed to adequately test potential treatment options. Vujanovic et. al. reviewed psychosocial therapies for depression and substance use disorders. The review discussed traditional psychotherapies such as cognitive behavioral therapy, as well as newer approaches such as mindfulnessand acceptance-based treatments. The authors concluded that the evidence base was, as might be expected, larger for the older than newer approaches (6). Two of the reviews focused on tobacco use. Smoking appears to be much more common in people with psychiatric illnesses than in the general population. Weinberger et. al. provided a critical review of the literature on the relationship between smoking and depression (7). The literature supporting a relationship between smoking and depression is strong. When present in smokers, depression was associated with poorer abstinence rates and greater smoking relapse. Keyser-Marcus et. al. reviewed the literature on impulsivity and cue reactivity and their relationship with tobacco use and depression and anxiety. Impulsivity and cue reactivity are strongly associated with smoking (8). However, impulsivity and cue reactivity in depressed or anxious people who use tobacco is not extensively researched. The review highlights the paucity of data in this area and the need for more research. With increased legalization, much attention has focused on the potential health consequences of cannabis use. Hanna et. al. reviewed the literature on whether cannabis use can lead to the development of a longlasting psychotic disorder (9). The authors concluded that the evidence supporting an association of cannabis use and the development of psychosis is strong. The implications of these conclusions are concerning and have substantial public health consequences. The reviewer, however, notes the limitations of the existing literature and the need for additional research to more clearly determine cause and effect and rule out potential confounding factors.