Despite evidence linking social connectedness (SC) and substance use disorders (SUD) treatment outcomes, there remains a gap in the literature about how people with SUD experience SC during music therapy. The purpose of this study was to understand how adults with SUD on an inpatient detoxification unit experienced SC during group-based songwriting. Participants were 12 adults with SUD who attended a single-group recovery-oriented songwriting session. After four sessions, we conducted individual semi-structured interviews with participants and used an inductive approach to thematic analysis to analyze interviews. Five themes emerged. The first two themes addressed how the songwriting session influenced SC: (1) songwriting facilitated participation and recognition of shared experiences with peers and (2) collaboratively creating a musical product was a positive experience that facilitated peer connections. Although not specific to the songwriting intervention, the final three themes described how social relationships, addiction, and recovery interacted and influenced each other more broadly: (3) addiction is associated with damaged relationships and isolation, (4) relationships and social support can aid or hinder recovery, and (5) reluctance to form relationships in treatment. Implications for clinical practice, limitations, and suggestions for future research are provided.