Understanding depression as biologically caused has been shown to impact both treatment preferences and prognostic pessimism. Attribution theory has been posited as an explanation for this relationship. Given that evidence‐based psychotherapy is effective yet often not delivered to individuals with depression, the present study sought to determine factors that impact treatment credibility. Non‐treatment‐seeking, depressed individuals (n = 229) were randomly assigned to read a psychoeducation article about depression that consisted of a biological causal explanation, psychosocial causal explanation, or a non‐causal control. Attributional dimensions of locus, stability, and control were examined as mediating the relationship between causal explanation and treatment credibility and prognostic pessimism. Individuals in the biological condition were more likely to find antidepressant medication a credible treatment for depression. The manipulation had no direct effect on preference for psychotherapy or prognostic pessimism. Attributional dimensions of locus, stability, and control did not mediate the relationship between causal explanation and treatment credibility. To the extent that the psychosocial article increased perceived instability of the depression cause, however, prognostic pessimism was reduced. The present study has implications for framing education about depression in mental health literacy programs and public awareness campaigns.