Hyperbaric medicine and the placebo effect.

The placebo in medicine has a long and interesting history. Despite the widespread use of placebo medication and sham interventions in clinical research, surprisingly little is known about how placebos work. There is evidence the administration of placebo preparations can induce measurable changes in physiology including the production of endorphins. Placebos usually involve some form of deception, but have been shown to work even when their lack of 'active' ingredients is declared to the patient. The relevance of the nature of placebo effects has become a central debate in the field of hyperbaric medicine with the recent suggestion that 131 kPa of air may be an active therapeutic intervention rather than a convenient and convincing sham. This paper discusses the nature of placebo and participation effects and the implications for hyperbaric oxygen therapy if low-pressure air is regarded as therapeutic.