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Logo of bmjThis ArticleThe BMJ
BMJ. 2008 May 17; 336(7653): 1086.
PMCID: PMC2386632
Placebo Effect

Reconceptualising placebo

G Lorimer Moseley, Nuffield medical research fellow

The notion that placebo responses are responses that are evoked by nothing is nonsense. The study by Kaptchuk et al and the study by Waber et al in JAMA illustrate clearly that the “placebo”’ responses observed are in fact responses to things other than the thing to which we hypothesise a response.1 2 Therefore, placebo responses reflect the limitations of our experimental design, our appreciation of the contributors to a patient’s symptoms, and our appreciation of what might change those underpinning factors. The convincing placebo data concern symptoms—experiences reported by patients. That means that symptoms are outputs of the brain. That a placebo response occurs means that something has changed the brain’s evaluation of whether or not to evoke that symptom. This makes a placebo response not a response to nothing, but to something we haven’t identified or measured. Take pain for example: it emerges according to an implicit evaluation of the threat to body tissue and the need for action. It is sensible that anything that changes this implicit evaluation of threat should change pain.

Rather than interpreting “placebo” responses as mysterious unexplainable responses to nothing, we should, as the editorial hints,3 get excited about what else might have led the patient’s brain to conclude that the need for symptoms had just reduced. To suggest we should use the placebo response in clinical practice seems a bit daft to me because it is the other things (we are yet to identify, accept, or understand), which change the brain’s evaluation of the need for symptoms, that we should utilise. I agree that the alternative therapies are way in front of us here—they know they are using some of these things, it just doesn’t make them conclude that what they do is useless.


Competing interests: None declared.


1. Kaptchuk TJ, Kelley JM, Conboy LA, Davis RB, Kerr CE, Jacobson EE, et al. Components of placebo effect: randomised controlled trial in patients with irritable bowel syndrome. BMJ 2008;336:999-1003. (3 May.) [PMC free article] [PubMed]
2. Waber RL, Shiv B, Carmon Z, Ariely D. Commercial features of placebo and therapeutic efficacy. JAMA 2008;299:1016-7. [PubMed]
3. Spiegel D, Harrington A. What is the placebo worth? BMJ 2008;336:967-8. (3 May.) [PMC free article] [PubMed]

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