Comorbidity of substance use and other psychiatric disorders--theoretical foundation and evidence based therapy

The coincidence of two or more psychiatric disorders in the same person (comorbidity or dual diagnosis) is no rare exception. It is rather common and therapeutically highly relevant. Comorbid patients exhibit frequently severe manifestations of the disorder(s) and they require intensive treatment to meet their special needs and the interdependencies of their disorders. The present overview deals with the theoretical foundations of comorbidity of substance use and other psychiatric disorders. We present data on the prevalence of different comorbidities and discuss the models, which have been proposed to explain how substance use and other disorders relate with each other. Furthermore, we describe the clinical characteristics and long-term course of comorbid patients, as well as some general therapeutic principles including the advantages of integrated therapeutic programmes. In addition, we carried out a systematic literature search on specific pharmaco- and psychotherapies for common comorbidities using the databases MEDLINE, EMBASE and PsycInfo (up to December 2007), and assessed the methodological quality of the identified trials. Based on this search we present the empirical evidence for the effectiveness of specific treatments and make therapeutic recommendations which are graded according to the strength of existing evidence. In conclusion, integrated treatment programs are more effective, provided they take into account the multiple deficits of comorbid patients, adjust and adapt the different therapeutic components to each other, and set realistic goals. The next step should be a broader application of integrated treatment programs and their adoption as standard treatment within the national health systems.