Introduction - Dual diagnosis (i.e., comorbid psychosis and substance use disorder) is characterized by more severe psychopathology, higher morbidity, less treatment adherence, and smaller treatment gains compared to psychosis alone. Further, there is a clear association between educational status and both prevalence and mortality of psychosis and substance use. Thus, the debilitating symptoms of these disorders propagate social inequality as well as being a substantial societal burden in purely economic terms. Importantly, this burden seems to increase when patients cannot access evidence-based treatment and recent policy changes mean that the amount of dual diagnosis patients in the Danish mental health services will soon more than triple. Improving the accessibility and efficacy of treatment for this vulnerable population is therefore more than ever, a critical unmet need. For this reason, this study aims to investigate the feasibility, efficacy, and acceptability of a partially auto-mated virtual reality (VR) based psychotherapeutic intervention targeting anxiety in dual diagnosis patients. Social avoidance has been theorized to be a highly relevant treatment target in dual diagno-ses populations since it is thought to play a critical role in maintaining symptoms, worsening mood and functional impairment, and deteriorating treatment adherence. Recent studies have found that VR-based cognitive behavioral therapy for psychosis (CBTp) resulted in significant reductions in anxiety and psychotic symptoms, while being safe and acceptable. Studies also show that this treatment can be automated, thus greatly increasing accessibility of treatment. Further, automatiza-tion allows patients to continue treatment even after hospital discharge, potentially maintaining treatment gains for longer. In short, there are several findings which indicate that automated VR-based CBTp is a promising treatment for dual diagnosis and therefore this present trial will be the first in the world to investigate this.

Background - Though CBTp has been shown to be an effective and safe treatment that patients prefer to medication, it is still poorly implemented in many countries. Only 0.07 % of the 5.5 billion DKK that schizophrenia costs Danish society yearly, are related to contacts with a psychologist or psychiatrist, implying that CBTp is also poorly implemented in Denmark. For dual diagnosis patients, prospects of receiving CBTp are further complicated because hospitals offering CBTp often forward patients with comorbid SUD to municipal services. In addition, the evidence supporting psychotherapy for dual diagnosis is still inadequate and the long-term effect of treat-ment remains unclear. This is likely because psychotherapy can be difficult to access for dual diag-nosis patients, being a long-term and complex intervention, which requires a high level of competence from the administering clinician. The lack of high quality clinical research, along with the complexity of the treatment, represent major barriers for implementation. Incorporating the use of VR technology in high quality clinical research may be one way to develop CBTp towards be-coming more accessible, increase long term efficacy and address anxiety symptoms, and easier to implement.