Elsevier

Mayo Clinic Proceedings

Volume 80, Issue 9, September 2005, Pages 1119-1121
Mayo Clinic Proceedings

EDITORIAL
What Is Controlled for in Placebo-Controlled Trials?

https://doi.org/10.4065/80.9.1119Get rights and content

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Factors That Produce Placebo Responses

For decades, placebo responses were conceptualized primarily as resulting from inert physical agents; however, explanations of placebo responses have shifted from environmental factors to human meanings and perceptions.4, 5 Placebo responses are produced by both external and experienced factors and the relationships between them.6

External Factors: The Roles of Conditioning and Suggestion. Previous experiences with symptoms, the remedy, and overall setting are likely to influence perception of

Neurobiology of Placebo Analgesia

The biological mechanisms whereby conditioning and expectancies may alter the experience of pain have been at least partially elucidated. Substantial evidence now indicates that under some circumstances, placebo analgesia is mediated by activation of endogenous opioids, suggested by the fact that naloxone, an opioid receptor antagonist, can reverse placebo responses.11, 12, 13 In 1 interesting study, a conditioning procedure was used to create placebo analgesia in the context of experimentally

Future Strategies for Assessing and Dealing with Placebo Responses in Clinical Studies and During Treatments

It is not commonly understood that clinical trials rarely measure the placebo effect. This is because having both active treatment and placebo conditions within a trial allows only a comparison between these 2 conditions. As noted previously, measurement of the placebo effect requires a comparison between the untreated natural history condition and the placebo condition. A meta-analysis of 27 unusual studies, primarily involving clinical trials that contained both natural history and placebo

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    Furthermore, under the PEMF, migraine intensity was not significantly different between responders and non-responders to placebo; thus, in placebo-responders, the effect of placebo was absent while using the PEMF. Two limitations of this cross-over approach are the absence of an isolated evaluation of placebo during the natural history of migraine2 and measurements of patients’ expectations.29 However, when migraine intensity and frequency were compared between patients on the first or the second treatment as a whole, there was no significant difference between the groups, suggesting that the first treatment was neither more nor less effective than the second; thus, the results are not likely to be dependent on an increased patients’ expectation on the first treatment or its loss at the second phase of the study.

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    The results of this open-label trial suggest that this proprietary treatment program is a promising outpatient medical treatment for methamphetamine dependence. However, given the potential biases associated with the open-label design and lack of placebo control, controlled studies are needed to establish the efficacy of the complete treatment program.40 In addition, controlled trials are needed to more fully assess the potential of the pharmacological agents used in this program for improving neurocognitive functioning in chronic methamphetamine abusers in early abstinence.

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See also pages 1126 and 1138

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