Objective: The main objective of this study was to explore the relationship between alliance and treatment outcome of substance use disorder (SUD) outpatients in routine care. Attachment, type of substance use, and treatment orientation were analyzed as potential moderators of this relationship.

Method: Ninety-nine SUD outpatients rated their psychological distress before every session. Patients and therapists rated the alliance after every session. At treatment start and end, the patient completed the Alcohol Use Disorders Identification Test (AUDIT), the Drug Use Disorders Identification Test (DUDIT), and the Experiences in Close Relationships (ECR-S). Data were analyzed using multilevel growth curve modeling and Dynamic Structural Equation Modeling (DSEM).

Results: The associations between alliance and outcome on psychological distress and substance use were, on average, weak. Within-patient associations between patient-rated alliance and outcome were moderated by self-rated attachment. Type of abuse moderated associations between therapist-rated alliance and psychological distress. No moderating effect was found for treatment orientation.

Conclusions: Patients' attachment style and type of abuse may have influenced the association between alliance and problem reduction. A larger sample size is needed to confirm these findings.