Dual diagnosis (substance use disorder combined with a comorbid mental illness) is a common problem. One of the methods to treat this is integrated dual diagnosis treatment (IDDT). IDDT consists of the simultaneous, integrated application of different treatment components. Their efficacy, however, has only been studied separately. As a result, the effectiveness of the IDDT program as a whole remains unclear.To evaluate the scientific evidence relevant to the effectiveness of IDDT in dual diagnosis patients.A systematic literature review using MEDLINE, Embase and PsycINFO (Prisma guideline).Six studies were found: a randomised controlled study (RCT), two non-randomised controlled studies, and three uncontrolled pre-post studies . There was a notably large diversity in outcome measures. The results differed significantly, including some studies concluding a significant (additional) effect, while others concluded that there was no indication of a significant effect of IDDT.In clinical practice, IDDT is recommended and chosen frequently as the treatment for patients with dual diagnosis. However, it is remarkable how limited and unthorough the research is pertaining to the effects of the full IDDT program on dual diagnosis.