This article presents a comprehensive review of the topic of placebos, with a special focus on placebo analgesia. It includes a discussion of how placebos work (the placebo effect) and how patients react to them (the placebo response). A literature search was performed to identify relevant literature and publications related to the topic, and a qualitative assessment of papers was undertaken based on accepted rules for scientific evidence. The major finding from this review was that concepts about placebo effects and responses have changed dramatically over the years, especially in more recent years. This has occurred primarily as a result of more sophisticated experimental protocols using placebos in clinical studies of patients in pain, as well as various studies involving normal subjects. Our understanding of the biological and psychological mechanisms underlying placebo effects has expanded significantly due to recent developments in the technology of brain imaging. Based on findings from brain-imaging analyses, we now know that placebo analgesia is definitely a real (ie, biologically measurable) phenomenon. It can be pharmacologically blocked and behaviorally enhanced, and these responses have been demonstrated to be similar to those elicited by administration of “real” analgesic substances. Psychological mechanisms involved in placebo analgesia include expectancy, meaning response, and classical conditioning. This article concludes with an emphasis on understanding therapeutic responses to various treatments for temporomandibular disorders (TMD). Acupuncture and splint therapy can be good examples of powerful placebos in the field of TMD, and both of these are discussed in detail. Present knowledge suggests that every treatment for pain contains a placebo component, which sometimes is as powerful as the so-called “active” counterpart. While the deceptive use of placebos must be considered unethical, every health provider who is treating pain patients must be aware of this important phenomenon in order to harness its huge potential. J OROFAC PAIN 2009;23:93–107.
Key words: acupuncture, brain imaging, expectancy, oral splints, placebo effect, TMD