Predictors of response to medication and cognitive therapy in the treatment of moderate to severe depression

Despite abundant empirical evidence demonstrating that cognitive therapy and antidepressant medications are effective treatments for depression, neither treatment appears to work equally well for all patients. In the three studies contained in this dissertation, I examined data from a recent clinical trial comparing cognitive therapy and antidepressant medications in order to identify variables associated with response to these two treatments. In the first study, I examined the differential effects of personality pathology on short-term response and longer-term sustained response in the two treatments. Patients without personality disorders responded better to cognitive therapy than to medication treatment, whereas the reverse was true for patients with a comorbid personality disorder. The positive response to medications among patients with personality disorders was sustained only when those patients were continued on medications during the 12 month follow-up. Patients with personality disorders who were withdrawn from medications evidenced an extremely low sustained response rate. In the second study, I investigated whether a comprehensive set of baseline patient characteristics was associated with treatment response Findings indicated that chronic depression, older age, and lower intelligence each predicted relatively poor response irrespective of the treatment that was received. In addition, three prescriptive predictors of treatment response were identified. Patients who were married, unemployed, or experiencing a relatively large number of life events evidenced superior response to cognitive therapy relative to medications. In the third study, I examined four subsets of depressive symptoms and found no evidence that the severity of these symptoms at intake predicted differential response to the two treatments. In addition, I examined change in the magnitude of these symptom sets over the course of treatment and found that cognitive therapy produced greater change in the atypical vegetative symptoms of depression (specifically hypersomnia) relative to medication treatment. Several prognostic and prescriptive predictors of treatment outcome were identified in this work. These findings, if replicated, would have clear clinical utility for the appropriate matching of treatments to patients. In addition, the pattern of findings should also help to refine theories that seek to explain the mechanisms through which these two treatments generate their therapeutic effects