Introduction: Cognitive behavioral therapy and dialectical behavior therapy (DBT) can be effective in treating adults with ADHD, and patients generally consider these interventions useful. While adherence, as measured by attendance at sessions, is mostly sufficient, adherence to therapy skills has not been assessed. Furthermore, the relationship between patient evaluation of therapy effectiveness, treatment adherence, and clinical outcomes is understudied.

Objective: This study aimed to examine treatment acceptability and adherence in relation to treatment outcomes in a large randomized controlled trial comparing a DBT-based intervention with a nonspecific active comparison, combined with methylphenidate or placebo.

Method: A total of 433 adult patients with ADHD were randomized. Participants reported how effective they found the therapy, and adherence was measured by attendance at therapy sessions and by self-reports. Descriptive, between-groups, and linear mixed model analyses were conducted.

Results: Participants rated psychotherapy as moderately effective, attended 78.40–94.37% of sessions, and used skills regularly. The best-accepted skills were sports and mindfulness. Groups receiving placebo and/or nonspecific clinical management rated their health condition and the medication effectiveness significantly worse than the psychotherapy and methylphenidate groups. Improvements in clinical outcomes were significantly associated with treatment acceptability. Subjective (self-reported) adherence to psychotherapy was significantly associated with improvements in ADHD symptoms, clinical global efficacy and response to treatment.

Discussion: These results further support the acceptability of DBT for adult ADHD and suggest the need to address adherence to treatment to maximize clinical improvements. Results may be limited by the retrospective assessment of treatment acceptability and adherence using an ad hoc instrument.