Objective: The use of psychoactive substances has been one of the most important global public health problems over the last few decades. Among the problems associated with substance use, dual diagnosis is one of the most relevant. This study aims to investigate the predictive validity of the GHQ-28 (General Health Questionnaire-28; "probable psychiatric cases") in relation to poor treatment outcome measured by (a) "early treatment dropout" and (b) "nonclinically relevant improvement at discharge." Methods: A longitudinal prospective design was used. A sample of 219 substance use disorder patients, who received treatment in a therapeutic community, was selected. Patients were assessed using the GHQ-28 and the outcome variables were registered. A hierarchical logistic regression model was performed to identify factors independently associated with the outcome measure ("early treatment dropout" and "nonclinically relevant improvement at discharge"). Results: Of the total sample, 79 subjects (36%) were considered "early treatment dropouts" and 56.6% (102) presented a "nonclinically relevant improvement at discharge." The two hierarchical logistic regression results show that being classified as a "probable psychiatric case" was significantly and directly associated with "early treatment dropout" and "nonclinically relevant improvement at discharge," as a poor in-treatment outcome indicator. Conclusions: The results of this study support the notion that the probable psychiatric cases identified by the GHQ-28 scale have a greater probability of "early treatment dropout" and have a greater probability of "nonclinically relevant improvement in discharge" of the therapeutic community. These data indicate that GHQ-28 is a suitable clinical instrument for predicting dropout and treatment effect in residential substance use disorder treatment.
Keywords: GHQ-28; dual diagnosis; outcome variable; predictive validity; substance abuse; therapeutic communities.