Pulling back the curtain on placebo: The search for a relationship between anxiety and placebo response
The prevalence of placebo effects as identified throughout history suggests that they are an archetypal feature of human experience. Because the design of current psychopharmacological research focuses heavily on establishing drug efficacy in studies controlled with placebo, any facet that may eventually be removed from the placebo response may yield needed clarity in future studies of experimental medication. Placebo response in clinical research and experimental drug trials has been described as ubiquitous; however, some medical conditions are more responsive to placebo than others. One such relationship that appears in the literature but has been scantly studied is the dynamic between anxiety and placebo response. This current research endeavor was guided by the hypothesis that patient anxiety at pre-test would demonstrate a positive relationship with measures of depression severity change scores following standardized treatment with a placebo. In order to test the strength of this relationship, archival data from clinical trials of the antidepressant medication Escitalopram were analyzed. Placebo response was measured by calculating global change scores on the pre- and post-test Hamilton Depression Rating Scale (HAM-D) following one week of single-blind placebo treatment. Principal components analysis was conducted and an interpretable subscale of the HAM-D depression measure emerged after oblique rotation. This subscale was used to assess pre-test patient somatic anxiety. Correlations between this somatic anxiety subfactor and change scores in core depression items of the HAM-D achieved r(128) = .14, p = .056. Insofar as correlations demonstrated that the relationship between anxiety and placebo response exists in the direction of the hypothesis, implications for the continued practice of pharmaceutical research and therapeutic placebo treatment are discussed.