Table 2.
Characteristics of included studies.
| Title | Author | Country | Year | Condition | N | Female sex. % | Mean age, years | Treatment | Control treatment | Duration | Number of prim. outcomes | Primary outcome used for meta-analysis | Rational for choice |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Open-label placebo treatment in chronic low back pain: a randomized controlled trial | Carvalho et al.30 | Portugal | 2016 | Chronic low back pain | 83 | 71 | 44 | OLP (n = 41) | Treatment as usual (n = 42) | 21 days | 2 | Roland Morris Disability Questionnaire | Most clinically relevant |
| Open-Label Placebo Treatment for Cancer-Related Fatigue: A Randomized-Controlled Clinical Trial | Hoenemeyer et al.31 | US | 2018 | Cancer-related fatigue | 74 | 67 | 57 | OLP (n = 39) | Treatment as usual (n = 35) | 21 days | 2 | Fatigue Symptom Inventory (FSI-14) | Most clinically relvant |
| Altered Placebo and Drug Labeling Changes the Outcome of Episodic Migraine Attacks | Kam-Hansen et al.32 | US | 2014 | Migraine attacks | 66 | 85 | 41 | OLP (n = 66) | No treatment (n = 66) (within subject) | 7 migraine attacks | 1 | Change in headache, pain score | Only primary outcome |
| Placebos without Deception: A Randomized Controlled Trial in Irritable Bowel Syndrome | Kaptchuk et al.21 | US | 2010 | Irritable bowel syndrome | 80 | 70 | 47 | OLP (n = 37) | No treatment (n = 43) | 21 days | 1 | IBSa Global Improvement Scale | Only primary outcome |
| Open-Label Placebo for Major Depressive Disorder: A Pilot Randomized Controlled Trial | Kelley et al.37 | US | 2012 | Major depressive disorder | 20 | 70 | 39 | OLP (n = 11) | Waitlist (n = 9) | 14 days | 1 | 17-item Hamilton scale for depression | Only primary outcome |
| Effects of open-label placebo on pain, functional disability and spine mobility in chronic back pain patients: a randomized controlled trial | Kleine-Borgmann et al.33 | Germany | 2019 | Chronic back pain | 122 | 72 | 59 | OLP (n = 63) | Treatment as usual (n = 59) | 21 days | 1 | Composite pain intensity score 0–10 | Only primary outcome |
| Open-Label placebo for the treatment of unipolar depression: Results from a randomized controlled trial. (in press) | Nitzan et al.34 | Israel | 2020 | Major depressive disorder | 38 | 74 | 50 | OLP (n = 18) | Treatment as usual (n = 20) | 28 days | 1 | QIDS | Only primary outcome |
| Open-label placebos for menopausal hot flushes—a randomized controlled trial | Pan et al.28 | Germany | 2020 | Menopausal hot flushes | 100 | 100 | 55 | OLP (n = 50) | No treatment (n = 50) | 4 weeks | 2 | Hot flush score | Most clinically relevant |
| Conditioned Placebo Dose Reduction: A new treatment in ADHD? | Sandler et al.19 | US | 2010 | ADHD | 93 | 22 | 10 | Dose reduced/Placebo (n = 33) | Reduced Dose (n = 29), Full Dose (n = 31)a | 8 weeks | 1 | IOWA Connoers Rating Scale (Parent Version) | Only primary outcome (parents closer to child) |
| Open-label use of placebos in the treatment of ADHD: a pilot study | Sandler and Bodfish20 | US | 2008 | ADHD | 26 | 27 | Not stated (range 7 to 15) | OLP (n = 26) | 50% of baseline medication (n = 26) (cross-over design) | 21 days | 4 | Seven-point clinical global impression | Includes different perspectives |
| Open-label placebos improve symptoms in allergic rhinitis: A randomized controlled trial | Schaefer et al.38 | Germany | 2016 | Allergic Rhinitis | 25 | 84 | 26 | OLP (n = 12) | Treatment as usual (n = 13) | 14 days | 2 | Symptoms (self-developed questionnaire) | Most clinically relevant |
| Why do open-label placebos work? A randomized controlled trial of an open-label placebo induction with and without extended information about the placebo effect in allergic rhinitis | Schaefer et al.35 | Germany | 2018 | Allergic Rhinitis | 46 | 80 | 25 | OLP with briefing (n = 13) OLP without briefing (n = 13) | TAU + (n = 9), TAU- (n = 11) | 14 days | 2 | Symptoms (self-developed questionnaire) | Most clinically relevant |
| Open-label placebo reduces fatigue in cancer survivors: a randomized trial | Zhou et al.36 | China | 2019 | Cancer-Related Fatigue | 40 | 92 | 47 | OLP (n = 20) | No treatment (n = 20) | 21 days | 1 | Functional Assessment of Chronic Illness Therapy-Fatique (FACIT-F) | Only primary outcome |
IBS irritable bowel syndrom.
a“Full dose group” was excluded. We only compared the “reduced dose” group to the “reduced dose + placebo” group, which was scored as TAU.