Differences in cognitive factors between “true drug” versus “placebo pattern” response to fluoxetine as defined by pattern analysis

Abstract

Pattern analysis has identified two types of response patterns to antidepressants: "true drug" response (TDR) and "placebo pattern" response (PPR). This study examines the relationship between cognitive factors and TDR and PPR to fluoxetine. We assessed 310 outpatients meeting DSM-III-R criteria for major depressive disorder (MDD) who were enrolled in an 8-week open trial of fluoxetine 20 mg/day. Response patterns were determined using the clinical global impressions-improvement (CGI-I). We administered the following self-rated scales to all patients at the baseline visit and at endpoint: perceived stress scale (PSS), cognitions questionnaire (CQ), Beck hopelessness scale (BHS) and dysfunctional attitudes scale (DAS). One hundred and thirty-four patients had TDR, 66 patients had PPR, and 110 patients were non-responders (NR). Demographic variables and severity of depression at baseline (HAMD-17) were not significantly different between the two response pattern groups. We compared cognitive factors before and after treatment across patients with TDR and PPR, and there were no significant differences at baseline in CQ, PSS, BHS, and DAS scores. At endpoint, outpatients with PPR had significantly lower scores on the PSS (p < 0.001) compared to the patients with TDR, even after adjusting for multiple comparisons and severity of depression at endpoint. Significant differences in cognitive/psychological factors, specifically lower post-treatment perceived stress, accompany "placebo" pattern of response to antidepressant treatment and differentiate it from "true drug" response pattern, as defined by pattern analysis.