title: Which factors predict placebo response in anxiety disorders and major depression? An analysis of placebo-controlled studies of escitalopram.
abstract: BACKGROUND
  The placebo response rate has increased in several psychiatric disorders and is a major issue in the design and interpretation of clinical trials. The current investigation attempted to identify potential predictors of placebo response through examination of the placebo-controlled clinical trial database for escitalopram in 3 anxiety disorders and in major depressive disorder (MDD).
  
  
  METHODS
  Raw data from placebo-controlled studies (conducted from 2002 through the end of 2004) of escitalopram in patients meeting DSM-IV criteria for MDD and anxiety disorders (generalized anxiety disorder [GAD], social anxiety disorder [SAD], panic disorder) were used. Potential predictors examined were type of disorder, location of study, dosing regimen, number of treatment arms, gender of patients, and duration and severity of disorder.
  
  
  RESULTS
  Placebo response (defined as the percent decrease from baseline in the reference scale) was higher in GAD and MDD studies conducted in Europe (p < .0001 and p = .0006, respectively) and was not associated with gender or duration of episode. In GAD, the placebo response rate was higher in a European fixed-dose study, which also had more treatment arms. In SAD and in U.S. specialist-treated MDD, a higher placebo response rate was predicted by decreased baseline disorder severity.
  
  
  CONCLUSIONS
  Additional work is needed before definitive recommendations can be made about whether standard exclusion criteria in clinical trials of antidepressants, such as mild severity of illness, maximize medication-to-placebo differences. This analysis in a range of anxiety disorders and MDD suggests that there may be instances in which the predictors of placebo response rate themselves vary across different conditions.
authors.affiliation: Department of Psychiatry, University of Cape Town, South Africa. dan.stein@curie.uct.ac.za
authors.forename: Dan J
authors.initials: DJ
authors.lastname: Stein
authors.forename: David S
authors.initials: DS
authors.lastname: Baldwin
authors.forename: Ornah T
authors.initials: OT
authors.lastname: Dolberg
authors.forename: Nicolas
authors.initials: N
authors.lastname: Despiegel
authors.forename: Borwin
authors.initials: B
authors.lastname: Bandelow
mesh_terms: D000328:Adult; D000928:Antidepressive Agents / Q000008:administration & dosage*; D001008:Anxiety Disorders / Q000145:classification / Q000188:drug therapy*; D015283:Citalopram / Q000008:administration & dosage*; D003865:Major Depressive Disorder / Q000145:classification / Q000188:drug therapy*; D005260:Female; D006801:Humans; D008297:Male; D015990:Placebo Effect; D016896:Treatment Outcome
chemical_list: D000928:Antidepressive Agents; D015283:Citalopram