Disclosing the potential impact of placebo controls in antidepressant trials.

Background: Although placebo-control clinical trials that withhold effective treatments can be permissible, how best to inform participants of the placebo design has received little attention.

Aims: To determine the effect of disclosing quantitative outcome estimates of individual treatment . entering placebo-control randomised control trial (RCT) on willingness to enrol in such an RCT.

Method: We randomised 278 adult patients at a depression clinic to receive standard disclosure ( = 129) or enhanced ( = 149) quantitative outcome estimates (based on decision analysis) of individual treatment . RCT, and assessed their willingness to enrol in the RCT.

Results: A greater proportion of those in the standard arm preferred enrolling in RCT (41.3% . 23.8%, = 0.002). Those in the standard arm preferred RCT more for direct benefit than altruism reasons, whereas the opposite was true in the enhanced arm.

Conclusions: Disclosing the quantitative outcome implications of placebos may select for fewer but more altruistic participants.

Declaration Of Interest: S.Y.H.K. was a DSMB member of a clinical trial sponsored by Hoffman-LaRoche and he receives royalties from Oxford University Press for his book . C.M. has served in the past year on a scientific advisory board and as a consultant for Janssen Pharmaceuticals.

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