Does inclusion of a placebo arm influence response to active antidepressant treatment in randomized controlled trials? Results from pooled and meta-analyses.
OBJECTIVE
To determine if the inclusion of a placebo arm and/or the number of active comparators in antidepressant trials influences the response rates of the active medication and/or placebo.


METHODS
Searches of MEDLINE, PsycINFO, and pharmaceutical Web sites for published trials or trials conducted but unpublished between January 1996 and October 2007.


METHODS
2,275 citations were reviewed, 285 studies were retrieved, and 90 were included in the analysis. Trials reporting response and/or remission rates in adult subjects treated with an antidepressant monotherapy for unipolar major depression were included.


METHODS
The primary investigator recorded the number of responders and/or remitters in the intent-to-treat population of each study arm or computed these numbers using the quoted rates.


RESULTS
Poisson regression analyses demonstrated that mean response rate for the active medication was higher in studies comparing 2 or more active medications without a placebo arm than in studies comparing 2 or more active medications with a placebo arm (65.4% vs 57.7%, P < .0001) or in studies comparing only 1 active medication with placebo (65.4% vs 51.7%, P = .0005). Mean response rate for placebo was significantly lower in studies comparing 1 rather than 2 or more active medications (34.3% vs 44.6%, P = .003). Mean remission rates followed a similar pattern. Meta-analysis confirmed results from the pooled analysis.


CONCLUSIONS
These data suggest that antidepressant response rates in randomized control trials may be influenced by the presence of a placebo arm and by the number of treatment arms and that placebo response rates may be influenced by the number of active treatment arms in a study.
Sinyor
Mark
M
Department of Psychiatry, University of Toronto, Ontario, Canada.
Levitt
Anthony J
AJ
Cheung
Amy H
AH
Schaffer
Ayal
A
Kiss
Alex
A
Dowlati
Yekta
Y
Lanctôt
Krista L
KL
D000328:Adult; D000928:Antidepressive Agents / Q000627:therapeutic use*; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000188:drug therapy* / Q000523:psychology; D004311:Double-Blind Method; D006801:Humans; D015201:Meta-Analysis as Topic; D018579:Patient Selection; D015990:Placebo Effect; D010919:Placebos; D011569:Psychiatric Status Rating Scales / Q000706:statistics & numerical data; D016032:Randomized Controlled Trials as Topic; D012044:Regression Analysis; D012074:Remission Induction; D012107:Research Design; D016896:Treatment Outcome
D000928:Antidepressive Agents; D010919:Placebos