Examining the relationship between pre-treatment anhedonia and treatment outcomes in individuals with anxiety or depression: A systematic review

Anxiety and depressive disorders are the most common mental health conditions globally, contributing to substantial functional impairment across social and occupational domains. Despite the efficacy of first-line psychosocial (e.g., cognitive behavioral therapy) and biological (e.g., pharmacotherapy, transcranial magnetic stimulation) interventions, approximately half of patients fail to achieve clinically significant improvement. Identifying predictors of treatment outcomes is crucial for enhancing therapeutic efficacy and addressing limitations of current treatments. This systematic review aimed to synthesize the literature on the relationship between pre-treatment anhedonia and treatment response in individuals receiving psychotherapy, pharmacotherapy, or neuromodulation for anxiety or unipolar depressive disorders. Studies were included that assessed the clinical symptom of anhedonia using subjective measures and, secondarily, subjective, neural, or behavioral indicators of reward sensitivity. Of the 28 articles meeting criteria for this review, nine (32.1 %) indicated higher anhedonia/lower reward sensitivity was associated with worse treatment response. Four studies (14.3 %) found it was linked to better outcomes, eleven (39.3 %) reported mixed results, and four (14.3 %) found no significant relationships. Definitive conclusions cannot be drawn given inconsistent findings and because most studies involved secondary analyses that were often inadequately powered, and there was substantial heterogeneity in treatment types, study designs, measurement approaches, and outcomes. Prospective studies explicitly designed and powered to test anhedonia as a treatment predictor are needed. Future research should also clarify the direction, strength, and clinical relevance of the relationship between anhedonia - including its subcomponents and various units of analysis - and treatment outcomes in depression, anxiety, and related conditions.