Specific and common processes as mediators of the long-term effects of cognitive-behavioral therapy integrated with motivational interviewing for generalized anxiety disorder

OBJECTIVE: A trial of psychotherapy for generalized anxiety disorder (GAD) demonstrated that motivational interviewing (MI) integrated with cognitive-behavioral therapy (CBT) outperformed CBT alone on clients' worry reduction across a 12-month follow-up. In the present study, we hypothesized and tested that less client resistance and greater client-perceived therapist empathy (specific foci of MI) would account for MI's additive effect. Exploratory analyses assessed whether the common processes of homework completion and therapeutic alliance quality mediated the treatment effect. METHOD: Clients with GAD were randomized to 15 sessions of MI-CBT (n = 42) or CBT alone (n = 43). Worry was assessed throughout treatment and follow-up. Observers rated resistance at midtreatment, and clients reported on perceived therapist empathy, alliance, and homework completion throughout treatment. Mediation was tested with bootstrapping methods. RESULTS: Expectedly, MI-CBT clients evidenced less resistance and perceived greater therapist empathy, each of which related to lower 12-month worry. However, when both variables were tested simultaneously, only resistance remained a significant mediator of treatment. No indirect effects through homework completion or alliance emerged. CONCLUSIONS: Reducing client resistance may be a theory-consistent mechanism through which integrative MI-CBT promotes superior long-term improvement than traditional CBT when treating GAD. Clinical or methodological significance of this article: This study further supports the long-term clinical benefit of integrating MI into CBT when treating the highly prevalent and historically difficult-to-treat condition of GAD. In particular, it points to the theory-specific mechanism of MI (helping to reduce/resolve patients' in-treatment resistance) as accounting for the integrative treatment's additive effect on worry reduction across a follow-up period. Therapists using CBT to treat patients with GAD should be trained to incorporate MI principles (e.g., empathy, collaboration, autonomy support) in general and in response to explicit markers of resistance.