**5. Conclusions**

The present work represents a first contribution to the knowledge of the differential circadian characteristics of dual diagnosis patients taking into account their comorbid SMI, as well as the relationship with sociodemographic, clinical variables and treatment modality received for the SUD. The results obtained point out the importance to consider the circadian rhythmic expression in the clinical managemen<sup>t</sup> of dual patients, with residential treatment modality being a possible indicator of a better restoration of circadian functioning. Our findings may confirm the idea that the DST rhythm could be a biological marker of treatment adherence and a protective factor of the comorbid SMI disorder; even though future longitudinal studies are required to contrast such evidence. Progress in this line can contribute, firstly, to the detection of possible markers of vulnerability and, secondly, to establishing more appropriate therapeutic goals that incorporate chronotherapeutic strategies. All of this seems especially of interest for patients with greater circadian dysfunction such as those with SZ+, BD+ and under outpatient treatments, in whom the emphasis on maintaining changes in behavior and appropriate time habits may improve the response to treatment and prevent relapses.

**Author Contributions:** Conceptualization, A.A.; methodology, A.A. and J.F.N.; validation, A.A, A.B.S.-S. and J.E.M.-A.; formal analysis, A.A., A.B.S.-S. and A.M.-N.; investigation, A.B.S.-S., J.E.M.-A. and A.A.; writing—review and editing, all authors; funding acquisition, A.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Spanish Ministry of Economy, Industry and Competitiveness (PSI2015-65026-MINECO/FEDER/UE); Generalitat de Catalunya (2017SGR-748) and the Spanish Ministry of Science and Innovation (PID2020-117767GB-I00/AEI/10.13039/501100011033).

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by Ethics Committee of the University of Barcelona (IRB00003099).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** We thank the Mental Health division of Althaia Foundation, Gressol Man Project Foundation in Catalonia, ATRA group, Mental Health of Vall Hebron Hospital and Addiction's Division of the Maresme Health Consortium, Ethos Association, Center for Attention and Follow-up on Drug Dependencies Les Corts, Els Tres Turons Foundation, Septimània and Dianova Association for providing the sample of the study.

**Conflicts of Interest:** The authors declare no conflict of interest.
