Background:
No regulations govern placebo composition. The composition of placebos can influence trial outcomes and merits reporting.
Purpose:
To assess how often investigators specify the composition of placebos in randomized, placebo-controlled trials.
Data Sources:
4 English-language general and internal medicine journals with high impact factors.
Study Selection:
3 reviewers screened titles and abstracts of the journals to identify randomized, placebo-controlled trials published from January 2008 to December 2009.
Data Extraction:
Reviewers independently abstracted data from the introduction and methods sections of identified articles, recording treatment type (pill, injection, or other) and whether placebo composition was stated. Discrepancies were resolved by consensus.
Data Synthesis:
Most studies did not disclose the composition of the study placebo. Disclosure was less common for pills than for injections and other treatments (8.2% vs. 26.7%; P = 0.002).
Limitation:
Journals with high impact factors may not be representative.
Conclusion:
Placebos were seldom described in randomized, controlled trials of pills or capsules. Because the nature of the placebo can influence trial outcomes, placebo formulation should be disclosed in reports of placebo-controlled trials.
Primary Funding Source:
University of California Foundation Fund 3929—Medical Reasoning.
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Author, Article and Disclosure Information
Acknowledgment: The authors thank Stephanie Cham, BS, for reviewing and confirming the exclusion categories for excluded articles and Asbjørn Hrobjartsson, David Mant, Jeffery Aronson, and Michael Clarke for useful comments on earlier drafts of the manuscript.
Grant Support: By University of California Foundation Fund 3929–Medical Reasoning. The manuscript was revised while Dr. Howick was a recipient of a Medical Research Council/Economic and Social Research Council Interdisciplinary Postdoctoral Fellowship (G0800055).
Disclosures: None disclosed. Forms can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms/do?msNum=M10-1554.
Reproducible Research Statement:Study protocol and data set: Available from Dr. Golomb (e-mail, [email protected]). Statistical code: Available online at www.OpenEpi.com.
Corresponding Author: Beatrice A. Golomb, MD, PhD, University of California, San Diego, School of Medicine, 9500 Gilman Drive, #0995, La Jolla, CA 92093-0995; e-mail, [email protected].
Current Author Addresses: Dr. Golomb, Ms. Erickson, Ms. Koperski, and Ms. Sack: University of California, San Diego, School of Medicine, 9500 Gilman Drive, #0995, La Jolla, CA 92093-0995.
Dr. Enkin: 1001 Bay Street, Apt 2404, Toronto, Ontario M5S 3A6, Canada.
Dr. Howick: Centre for Evidence-Based Medicine, University of Oxford, Oxford OX3 7LF, United Kingdom.
Author Contributions: Conception and design: B.A. Golomb, J. Howick.
Analysis and interpretation of the data: B.A. Golomb, L.C. Erickson, S. Koperski.
Drafting of the article: B.A. Golomb, J. Howick.
Critical revision of the article for important intellectual content: B.A. Golomb, L.C. Erickson, S. Koperski, M. Enkin, J. Howick.
Final approval of the article: B.A. Golomb, L.C. Erickson, S. Koperski, D. Sack, M. Enkin, J. Howick.
Provision of study materials or patients: B.A. Golomb.
Statistical expertise: B.A. Golomb.
Obtaining of funding: B.A. Golomb.
Administrative, technical, or logistic support: B.A. Golomb, S. Koperski, J. Howick.
Collection and assembly of data: L.C. Erickson, S. Koperski, D. Sack.
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