Effectiveness of Integrated Dual Diagnosis Treatment (IDDT) in severe mental illness outpatients with a co-occurring substance use disorder

Integrating substance use disorder treatment with psychiatric treatment is considered more favourable then treating these disorders parallel or sequential, but the evidence base is inconclusive. We examined the effectiveness of Integrated Dual Diagnosis Treatment (IDDT) on substance use in severe mental illness outpatients with substance use disorders. IDDT is a collaborative, multidisciplinary team approach in which motivational interviewing is a key element. In addition, we also examined the effects of IDDT implementation on skills and knowledge of mental health care professionals. A randomized controlled stepped-wedge cluster trial was performed in 6 functional assertive cummunity treatment teams. We included 37 clinicians who were given a three-day IDDT training. Our primary outcome was days of substance use at follow up, 12 months after IDDT implementation. This was assessed in 154 included patients and was measured with the Measurement in the Addiction for Triage and Evaluation. After implementation of IDDT we found a reduction in the number of days patients used alcohol or drugs, but no improvements on other secondary outcomes such as psychopathology, functioning, therapeutic alliance or motivation to change. Also, IDDT training did not seem to improve clinicians' knowledge, attitudes and motivational interviewing skills. Effects on our secondary outcomes may have been limited by the absence of a training effect in our clinicians. Our study clearly underlines the complexity of disseminating IDDT and in particular motivational interviewing.