When biological explanations undermine confidence in psychotherapy: Identifying and countering causal discounting

Both laypeople and clinicians tend to judge psychotherapy as less effective when a mental disorder is attributed to biological causes. This tendency is unwarranted, given that the combination of medication and psychotherapy is generally considered the optimal treatment. Among the mechanisms proposed for this effect, the present study examines causal discounting, the assumption that biological causes are sufficient to explain symptoms, overlooking psychosocial causes. To counteract this assumption, we developed an intervention explaining how biological and psychosocial causes are interdependent. Three pre-registered studies found that laypeople with and without elevated depressive symptoms (Study 1: N = 428; Study 2: N = 566) and mental health clinicians (Study 3: N = 495) discounted psychosocial causes and rated psychotherapy as less effective upon learning that a depression case had biological causes. However, our intervention improved perceived psychotherapy effectiveness more than materials from the National Institute of Mental Health and a popular commercial health website (WebMD) listing both types of causes. These findings suggest that explaining the interplay between biological and psychosocial factors may help prevent biological explanations from inadvertently diminishing perceived effectiveness. Future studies can test the intervention in real-life settings with direct measures of psychotherapy uptake and adherence.