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REPRODUCIBILITY OF PLACEBO ANALGESIA ACROSS THE CONTEXTS OF CREAM AND PILL PLACEBOS.
[Thesis]. Manchester, UK: The University of Manchester; 2011.
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Abstract
ABSTRACTThe existence and characterization of the consistent placebo responder has remained debatable. This has recently stimulated interest in reliably identifying the psychological correlates of the placebo response in order to achieve a more comprehensive understanding of its underlying mechanisms. The prediction of placebo personality, which can facilitate equitable distribution of placebo responders across clinical trial arms, is only possible in the presence of a stable placebo response. A treatment group (n =46) was randomized into two subgroups and experimental placebo analgesia induced using inert cream and pill, in the guise of IBUPROFEN in conjunction with a conditioning paradigm. These two groups crossed over after a minimum of two weeks and the test was repeated. We measured the magnitude of placebo-induced reduction in pain ratings using a visual analogue scale as well as employing a battery of questionnaires to evaluate the psychological profile of placebo responders. We demonstrated that stability of placebo response is small across contexts by reproducing placebo response obtained with cream with pill (n=3). We present results showing significant main effect of placebo modality, F (14, 90) = 3.2713 P < 0.001 and placebo modality by session interaction F (14, 90) =3.2948, P < 0.001. Placebo induced reduction in pain ratings was significantly correlated with expectancy scores in the second session, p> 0.05. These data suggest that placebo responses may be determined by the interaction of type of therapy and individual expectancies. We propose that evaluating the behavioural, physiological as well as psychological measurements outlined in this study will lead to a greater understanding of the requirements for consistent placebo response.