title: Moderators of placebo response to antipsychotic treatment in patients with schizophrenia: a meta-regression.
abstract: BACKGROUND
  Variation in placebo response within and among clinical trials involving patients with schizophrenia can substantially affect conclusions about the efficacy of new antipsychotic medications. Therefore, it is of great importance to identify factors that moderate response to placebo in such trials.
  
  
  OBJECTIVE
  The objective of this meta-regression analysis was to estimate the effect of potential moderators of placebo response in randomized, short-term clinical trials involving patients with schizophrenia, schizoaffective disorder or schizophreniform disorder.
  
  
  METHODS
  Mean placebo response and potential moderators were extracted from 35 placebo-controlled, randomized trials of antipsychotic medications in patients with schizophrenia. Placebo response was defined as the absolute change in the Brief Psychiatric Rating Scale total score. Fixed-effects meta-regression was used to investigate between-trial variation in placebo response.
  
  
  RESULTS
  Trial duration accounted for a substantial proportion of the between-trial variation in response (27%), with greater improvement on placebo observed in shorter trials. Other variables showed insufficient variation across trials to permit any inferences regarding their relationships with placebo response.
  
  
  CONCLUSIONS
  Placebo-controlled trials of short duration (<6-8 weeks) are vulnerable to substantial placebo response. Recruiting patients with more severe pathology to mitigate placebo response does not appear to offer benefits and may even be counterproductive. Meta-analyses based on individual patient data offer the potential for much more detailed and inferentially sound exploration of factors affecting placebo response and are highly recommended.
authors.affiliation: Biological Psychiatry Program, Department of Psychiatry, University of Cincinnati College of Medicine, 231 Bethesda Avenue, P.O. Box 670559, Cincinnati, OH 45267-0559, USA. welgeja@email.uc.edu
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Welge
authors.forename: Paul E
authors.initials: PE
authors.lastname: Keck
mesh_terms: D000328:Adult; D014150:Antipsychotic Agents / Q000627:therapeutic use*; D010054:Brief Psychiatric Rating Scale / Q000592:standards; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D015990:Placebo Effect; D010919:Placebos / Q000627:therapeutic use*; D016032:Randomized Controlled Trials as Topic; D012559:Schizophrenia / Q000188:drug therapy*; D016896:Treatment Outcome
chemical_list: D014150:Antipsychotic Agents; D010919:Placebos