Summary of findings for the main comparison. Effect of placebo interventions across all clinical conditions (main findings).
| Outcomes |
Effect [1] (95% CI) |
No. of participants (studies) | Quality of the evidence | Comments |
| All clinical conditions (binary outcomes) | RR 0.93 (0.88 to 0.99) | 6041 (44) | Moderate | Moderate heterogeneity. No statistically significant differences between patient‐reported, and observer‐reported binary outcomes. No statistically significant effect on: pain, nausea, smoking or depression [2]. Out of three pain trials with low risk of bias (1109 patients), one German acupuncture trial found a large effect, and two trials found no effect [3]. |
|
All clinical conditions (continuous outcomes) |
SMD ‐0.23 (‐0.28 to ‐0.17) | 10,525 (158) | Moderate | Moderate heterogeneity. Statistically significant differences between patient‐reported, and observer‐reported outcomes, SMD ‐0.26 (‐0.32 to ‐0.19) versus ‐0.13 (‐0.24 to ‐0.02). Meta‐regression explained 54% of the variation in effect [3]. |
|
Pain [2] (continuous outcomes) |
SMD ‐0.28 (‐0.36 to ‐0.19) | 4154 (60) | Moderate | Moderate heterogeneity. Seven trials (1198 patients) had low risk of bias, but heterogeneity was substantial: four German acupuncture pain trials found large effects, and three other pain trials found negligible effects [3]. |
|
Nausea [2] (continuous outcomes) |
SMD ‐0.25 (‐0.46 to ‐0.04) | 452 (7) | Moderate | Low heterogeneity. The pooled result for all nausea trials was similar to the pooled result of the two nausea trials with low risk of bias [3]. |
|
Depression [2] (continuous outcomes) |
SMD ‐0.25 (‐0.55 to 0.05) | 324 (8) | Moderate | Moderate heterogeneity. The pooled result for all depression trials was similar to the result of the single depression trial with low risk of bias [3]. |
|
Other outcomes [2] (continuous outcomes) Smoking, dementia, obesity, hypertension, insomnia, anxiety, asthma, phobia) |
Range of SMD: ‐0.63 (‐1.17 to ‐0.08) to ‐0.16 (‐0.48 to 0.16) |
1317 (41) | Low | There was a statistically significant, but unreliable, effect on asthma and phobia [3]. |
[1]. RR: relative risk; SMD: standardised mean difference.
[2]. Clinical conditions studied in three trials or more.
[3]. See Additional tables.