Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 3 complete abstracts (439 words), 9 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
Any dummy medication or treatment. Although placebos originally were medicinal preparations having no specific pharmacological activity against a targeted condition, the concept has been extended to include treatments or procedures, especially those administered to control groups in clinical trials in order to provide baseline measurements for the experimental protocol.
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Sham Treatment.
Where it fits in the MeSH classification
- Broader topics
- Pharmaceutical Preparations; Therapeutics
Research landscape
PubMed indexes 36,245 records tagged with the MeSH heading “Placebos” (counts retrieved 2026-10-31). 1,244 of them (3.4%) were published from 2020 onward, and the busiest period so far is through 1999 with 20,397 records.
Reviews account for 2,295 records (6.3%) and meta-analyses for 823. Randomized controlled trials number 16,476 (45.5%) as a share of all records on the topic. Randomized trials make up a comparatively large share of this literature, which means many treatment questions have been tested directly.
Show the data
| Period | Records |
|---|---|
| through 1999 | 20,397 |
| 2000-2009 | 8,200 |
| 2010-2019 | 6,404 |
| 2020 onward | 1,244 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 2,295 | 6.3% |
| Meta-analyses | 823 | 2.3% |
| Randomized controlled trials | 16,476 | 45.5% |
Method: PubMed query "Placebos"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-31.
Reading the evidence in drugs and chemicals
Studies of a chemical or drug can answer very different questions: what it is and how it behaves in cells and animals, how the body handles it, and whether it changes outcomes in people. Laboratory and animal findings often do not carry over to patients, and observational studies of exposures are confounded by who uses a substance and why. Nothing on this page is a recommendation to use, avoid, start or stop any substance or medicine; talk to a qualified clinician or pharmacist about your own situation. Check the dose, the species, the comparison group and whether a patient-relevant outcome was measured.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
| Study / authors | Year | Source label / design | Europe PMC citations | Licence / source |
|---|---|---|---|---|
| Effects of open-label placebos in clinical trials: a systematic review and meta-analysis | 2021 | Meta-analysis Design not recorded in structured metadata | 132 | cc by PMID 33594150 · DOI · PMC7887232 |
| Brain and psychological determinants of placebo pill response in chronic pain patients | 2018 | Research article Design not recorded in structured metadata | 97 | cc by PMID 30209286 · DOI · PMC6135815 |
| Attention placebo control in randomized controlled trials of psychosocial interventions: theory and practice | 2015 | Randomized controlled trial Design not recorded in structured metadata | 57 | cc by PMID 25872619 · DOI · PMC4404062 |
Effects of open-label placebos in clinical trials: a systematic review and meta-analysis [1]
Abstract reading summary — source excerpts
- Opening excerpt
- Open-label placebos (OLPs) are placebos without deception in the sense that patients know that they are receiving a placebo.
- Closing excerpt
- More research is needed, especially with respect to different medical and mental disorders and instructions accompanying the OLP administration as well as the role of expectations and mindsets.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (199 words)
Open-label placebos (OLPs) are placebos without deception in the sense that patients know that they are receiving a placebo. The objective of our study is to systematically review and analyze the effect of OLPs in comparison to no treatment in clinical trials. A systematic literature search was carried out in February 2020. Randomized controlled trials of any medical condition or mental disorder comparing OLPs to no treatment were included. Data extraction and risk of bias rating were independently assessed. 1246 records were screened and thirteen studies were included into the systematic review. Eleven trials were eligible for meta-analysis. These trials assessed effects of OLPs on back pain, cancer-related fatigue, attention deficit hyperactivity disorder, allergic rhinitis, major depression, irritable bowel syndrome and menopausal hot flushes. Risk of bias was moderate among all studies. We found a significant overall effect (standardized mean difference = 0.72, 95% Cl 0.39-1.05, p 2 = 76%) of OLP. Thus, OLPs appear to be a promising treatment in different conditions but the respective research is in its infancy. More research is needed, especially with respect to different medical and mental disorders and instructions accompanying the OLP administration as well as the role of expectations and mindsets.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 33594150 · DOI · PMC7887232
Brain and psychological determinants of placebo pill response in chronic pain patients [2]
Abstract reading summary — source excerpts
- Opening excerpt
- The placebo response is universally observed in clinical trials of pain treatments, yet the individual characteristics rendering a patient a 'placebo responder' remain unclear.
- Closing excerpt
- These results shed light on psychological, neuroanatomical, and neurophysiological principles determining placebo response in RCTs in chronic pain patients, and they suggest that the long-term beneficial effects of placebo, as observed in clinical settings, are partially predictable.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (143 words)
The placebo response is universally observed in clinical trials of pain treatments, yet the individual characteristics rendering a patient a 'placebo responder' remain unclear. Here, in chronic back pain patients, we demonstrate using MRI and fMRI that the response to placebo 'analgesic' pills depends on brain structure and function. Subcortical limbic volume asymmetry, sensorimotor cortical thickness, and functional coupling of prefrontal regions, anterior cingulate, and periaqueductal gray were predictive of response. These neural traits were present before exposure to the pill and most remained stable across treatment and washout periods. Further, psychological traits, including interoceptive awareness and openness, were also predictive of the magnitude of response. These results shed light on psychological, neuroanatomical, and neurophysiological principles determining placebo response in RCTs in chronic pain patients, and they suggest that the long-term beneficial effects of placebo, as observed in clinical settings, are partially predictable.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 30209286 · DOI · PMC6135815
Attention placebo control in randomized controlled trials of psychosocial interventions: theory and practice [3]
Abstract reading summary — source excerpts
- Opening excerpt
- UnlabelledAttention placebo control (APC) is considered a highly valid control condition when conducting trials of social interventions.
- Closing excerpt
- gov NCT02313493 : registered 10 December 2014.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (97 words)
UnlabelledAttention placebo control (APC) is considered a highly valid control condition when conducting trials of social interventions. Unfortunately, an appropriate APC condition is rarely used. This letter discusses the tension between methodological and ethical requirements of an APC group in psychosocial interventions based on our experiences with a randomized controlled efficacy study of a parent training program. To prevent negative side effects and high drop-out rates, feasible and accepted attention control conditions are discussed. The paradigms of placebo research must be adapted to the special challenges of psychosocial intervention research.Trial registrationClinicaltrials.gov NCT02313493 : registered 10 December 2014.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 25872619 · DOI · PMC4404062
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article Biological, clinical, and ethical advances of placebo effects [4]
- Research article The importance of placebo effects in pain treatment and research [5]
- Research article Neurobiological mechanisms of the placebo effect [6]
- Research article Waiting list may be a nocebo condition in psychotherapy trials: a contribution from network meta-analysis [7]
- Research article Placebos and painkillers: is mind as real as matter? [8]
- Research article Comparative efficacy and safety of biologic therapies for moderate-to-severe Crohn's disease: a systematic review and network meta-analysis [9]
References
- von Wernsdorff M, Loef M, Tuschen-Caffier B, Schmidt S. Effects of open-label placebos in clinical trials: a systematic review and meta-analysis. . 2021. PMID 33594150 · DOI · PMC7887232
- Vachon-Presseau E, Berger SE, Abdullah TB, Huang L, Cecchi GA, Griffith JW, et al.. Brain and psychological determinants of placebo pill response in chronic pain patients. . 2018. PMID 30209286 · DOI · PMC6135815
- Popp L, Schneider S. Attention placebo control in randomized controlled trials of psychosocial interventions: theory and practice. . 2015. PMID 25872619 · DOI · PMC4404062
- Finniss DG, Kaptchuk TJ, Miller F, Benedetti F. Biological, clinical, and ethical advances of placebo effects. Lancet. 2010. PMID 20171404 · DOI · PMC2832199
- Turner JA, Deyo RA, Loeser JD, Von Korff M, Fordyce WE. The importance of placebo effects in pain treatment and research. JAMA. 1994. PMID 7880221 · DOI
- Benedetti F, Mayberg HS, Wager TD, Stohler CS, Zubieta JK. Neurobiological mechanisms of the placebo effect. J Neurosci. 2005. PMID 16280578 · DOI · PMC6725834
- Furukawa TA, Noma H, Caldwell DM, Honyashiki M, Shinohara K, Imai H, et al.. Waiting list may be a nocebo condition in psychotherapy trials: a contribution from network meta-analysis. Acta Psychiatr Scand. 2014. PMID 24697518 · DOI
- Colloca L, Benedetti F. Placebos and painkillers: is mind as real as matter?. Nat Rev Neurosci. 2005. PMID 15995725 · DOI
- Singh S, Murad MH, Fumery M, Sedano R, Jairath V, Panaccione R, et al.. Comparative efficacy and safety of biologic therapies for moderate-to-severe Crohn's disease: a systematic review and network meta-analysis. Lancet Gastroenterol Hepatol. 2021. PMID 34688373 · DOI · PMC8933137
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-31.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.