[Double diagnosis or comorbidity? Definition and clinical observation]

There is a high prevalence of a comorbid substance use disorder in subjects with psychotic or mood disorders. Psychiatric patients are reported to abuse alcohol or drugs. This comorbidity raises the question whether one disorder is a consequence of the other. The self-medication hypothesis of substance abuse suggests that drug abuse is driven by an attempt to alleviate specific psychological distress but this unidirectional causality is not supported. The main aims of this review are to describe the difference between dual diagnosis and comorbidity in psychiatric patients and the possible patterns of different clinical conditions.