SynthesisBritish journal of clinical pharmacology2022
How do they add up? The interaction between the placebo and treatment effect: A systematic review.
Synthesis in British journal of clinical pharmacology, 2022. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 13 papers, 1 of them a synthesis that pooled it.
What it found
Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.
The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
The trial behind it
Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.
Who cites it
13 citing papers in PubMed, 1 synthesis or guideline pooled it, 33 citations in OpenAlex.
- How do they add up? The interaction between the placebo and treatment effect: A systematic review.British journal of clinical pharmacology · 2022Pooled it
- Effects of Hidden Conditioning and Positive Expectations on Pain Intensity Following Spinal Manipulative Therapy: A Three-Arm Randomized Controlled Trial.European journal of pain (London, England) · 2026Trial
- Placebo effects of transcranial direct current stimulation on motor skill acquisition.Neuroscience letters · 2023Trial
- Article
- Open-label placebos for low back pain: unresolved challenges and next steps.Pain management · 2025Article
- Is It All in Your Head? Placebo Effects in Concussion Prevention.Sports medicine (Auckland, N.Z.) · 2025Review
- The reliability and validity of the depression change expectancy scale in college students: a cross-sectional study in China.Scientific reports · 2025Article
- Placebo and nocebo effect in pain.Handbook of clinical neurology · 2025Review
- Contextual effects in musculoskeletal pain: are we overlooking essential factors?Frontiers in psychology · 2025Article
- Decoding the impact of the placebo response in clinical trials for chronic cough.ERJ open research · 2024Article
- Efficacy and Safety of Trazodone and Gabapentin Fixed-Dose Combination in Patients Affected by Painful Diabetic Neuropathy: Randomized, Controlled, Dose-Finding Study.Pain and therapy · 2024Article
- Harnessing placebo: Lessons from psychedelic science.Journal of psychopharmacology (Oxford, England) · 2023Review
- Effect of a Multi-Strain Probiotic on Secretory Immunoglobulin-A Levels in Patients with Complete Edentulism: A Quasi-Experimental Study.Journal of International Society of Preventive & Community DentistryArticle
Corrections and comments
PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.
Authors and funding
10 authors at 7 institutions in 2 countries.
Funding
Abstract
aimThe placebo effect and the specific effect are often thought to add up (additive model). Whether additivity holds can dramatically influence the external validity of a trial. This assumption of additivity was tested by Kleijnen et al in 1994 but the data produced since then have not been synthetized. In this review, we aimed to systematically review the literature to determine whether additivity held.
methodsWe searched Medline and PsychInfo up to 10 January 2019. Studies using the balanced placebo design (BPD), testing two different strengths of placebos, were included. The presence of interaction was evaluated by comparing each group in the BPD with analysis of variance or covariance.
resultsThirty studies were included and the overall risk of bias was high: four found evidence of additivity and 16 studies found evidence of interaction (seven had evidence of positive additivity).
conclusionEvidence of additivity between placebo and specific features of treatments was rare in included studies. We suggest interventions for placebo-sensitive ailments should be tested in trials designed to take interactions seriously once an exploratory RCTs has proven their efficacy with sufficient internal validity.
Indexed as
Identifiers
What OpenQuestion holds
Registered trials
Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.