Introduction: While the reporting of Randomized Controlled Trials (RCT's) is being standardised and improved, the role of the placebo effect is often not considered when reporting the results of these trials. By not taking account of the power of placebo effects authors and readers risk misinterpreting the results of RCT's.

Objective: Examples of the power of placebo effects will be presented and several theories of placebo mechanisms will be examined. Proposed theories of placebo action include conditioning, faith, expectation, design and measurement artefacts, anxiety reduction, homeostatic-cybernetic self regulation, and symbolic processes (White, Tursky & Schwartz, 1985). The implications of the conditioning theory of placebo action will be examined in detail. By understanding how placebo effects can be generated it is possible to better take account of these factors. The conditioning model of pharmacotherapy suggests there may be a 'psychological carryover effect' which is distinct from any pharmacokinetic influence when active medication is presented first (Ader, 1993).

Methods: Examples of RCT's that have inadvertently maximised the placebo effect will be presented, along with possible explanations from differing theoretical perspectives, in order to demonstrate how unjustifiable conclusions can be drawn from the results of RCT's when the power of placebos is not adequately considered.

Results: While placebo effects should no longer be considered 'nuisance variables', an understanding of how they can be generated makes it possible to better take account of their potential effects.