Background: The incidence of dual diagnosis (DD) (i.e. substance use disorders [SUD] and co-occurring mental disorders) is widespread; however, they vary widely in permutation and combination. As a result, establishing effective and empirically supported interventions for this clinical population remains challenging.Aim: This study aimed to examine current literature on the treatment outcomes for patients with DD.Method: A systematic review of randomised controlled trials (RCTs) published between 2009 and 2018 was conducted for two broad intervention categories identified by the literature: non-integrated and integrated treatment. Multiple electronic databases were searched using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines (PRISMA).Results: The search generated a total of 743 studies, of which 11 satisfied the inclusion criteria. These studies were thematically synthesised into two main analytical themes: ‘treatment outcomes’ and ‘reported strengths and limitations of DD treatment’. Specifically, integrated treatment held an advantage over non-integrated treatment in significantly improving psychiatric symptomatology. However, no significant benefits were found between integrated and non-integrated treatment regarding substance misuse and treatment retention.Conclusion: Overall, the results provided insufficient evidence to support the enhanced efficacy of integrated or non-integrated treatment over the other in treating patients with DD.Contribution: The study’s findings were used to provide recommendations to inform the clinical psychological service delivery of dual diagnosis treatment in South Africa and also to identify gaps in the literature and highlight areas for future research.