The impact of comorbid substance use on individual and group therapeutic alliance in specialised personality disorder treatment: a longitudinal multi-site study

Abstract

Abstract Background The therapeutic alliance remains understudied in patients with personality disorders and comorbid substance use disorders. While personality disorder alone has been associated with impaired alliance formation and quality, the specific contribution of comorbid substance use to alliance quality is poorly understood. This study investigates how comorbid substance use may impact the therapeutic alliance in personality disorder. Methods Longitudinal data were retrieved from a multi-site study of patients with personality disorders undergoing treatment during 2017–2022. The study included 742 participants and examined group and individual alliance. Mental disorders were assessed at baseline by structured interviews (SCID-5-PD, MINI). Substance use was assessed using DUDIT-3 and AUDIT-C at baseline and at six-month intervals throughout treatment. Alliance assessment included patient self-reports on individual therapy alliance (WAI-SF) and group therapy alliance (GQ), collected at six-month intervals. Data were analysed using three-level hierarchical linear mixed models (HLM), with repeated alliance assessments nested within patients, and treatment centres. Results When including time of assessment, personality disorder, other mental disorders, gender, age, and treatment context, significant negative relationships were demonstrated between within-person substance use and alliance measure: GQ work. No significant associations were found between SUD and total alliance scores or bond in group or individual treatment. Trends were identified for a negative association between SUD and tasks and goals in the individual alliance. Associations were not significant for AUDIT-C. Conclusions The results demonstrate that higher substance use relative to a person’s own mean could be a significant patient characteristic that impedes the group therapeutic alliance in patients. The study finds that the association between substance use and therapeutic alliance may be weaker than reported in the literature. The study explicitly points to poorer mutuality in collaboration in group treatments. Clinical trial number Not applicable.