**5. Conclusions**

Our study shows that DD is a prevalent issue among individuals with alcohol or cocaine use disorders and could influence their dropout from treatment in public outpatient drug dependence care centres, along with alcohol use, polysubstance use and social conditions, such as living alone. We have designed a new large-scale study, which introduces all the above changes and an extended follow-up to confirm these preliminary results. We believe that introducing DD evaluation in the routine biopsychosocial assessments of individuals with a SUD when starting treatment could help the design of more tailored treatment strategies and improve the prognosis of those individuals.

**Author Contributions:** Conceptualisation, M.T.B.; formal analysis, B.P.-G.; investigation, L.T., C.R.-D., J.M.V.-V., A.P., M.C.-G., M.J.-D., I.O., E.G., N.M. and The Dual Diagnosis Study Group; writing— original draft preparation, B.P.-G.; writing—review and editing, B.P.-G., M.G.B., M.B., M.T.B., M.G., O.P.-B. and M.T.; visualisation, B.P.-G.; supervision, M.G.B., M.B., M.T.B. and M.T.; project administration, M.T.B., M.B. and M.G.B.; funding acquisition, M.T.B. and M.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by: Instituto de Salud Carlos III, PI16/01075; Instituto de Salud Carlos III—European Regional Development Fund -Red de Trastornos Adictivos (RTA), UE-FEDER 2016 RD16/0017/0010; Instituto de Salud Carlos III, Redes de Investigación Cooperativa Orientadas a Resultados en Salud (RICORS), Red de Investigación en Atención Primaria (RIAPAd), RD21/0009/0001 and the European Union NextGenerationEU, Mecanismo para la Recuperación y la Resiliencia (MRR).

**Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki and approved by The Parc de Salut Mar Clinical Research Ethics Committee (Barcelona, Spain) (2019/6422/I).

**Informed Consent Statement:** Written informed consent was obtained from all participants involved in the study during the first treatment visit in the drug dependence care centres.

**Data Availability Statement:** The data that support the findings of this study are not publicly available but are available from the corresponding author (M.G.B) upon reasonable request.

**Acknowledgments:** We thank Gail Craigie for editorial assistance and Carlos García Forero for his valuable comments during the analysis of the article.

**Conflicts of Interest:** M.T. is a co-author of this paper and member of the Recent Advances in Dual Disorders (Addiction and Other Mental Disorder) Special Issue of the Journal of Clinical Medicine. The rest of the authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.