1. Effect of placebo interventions across all clinical conditions (binary outcomes).

	All trials			Trials with low risk of bias			Quality of the evidence
Outcomes	Relative Risk (95% CI)	No. of participants (studies)	Comments	Relative Risk (95% CI)	No. of participants (studies)	Comments
All clinical conditions	0.93 (0.88 to 0.99)	6041 (44)	Symmetrical funnel plot Moderate heterogeneity	0.90 (0.76 to 1.08)	1,438 (5)	Substantial heterogeneity. One German acupuncture trial found RR 0.69 (0.61 to 0.78) and the other four trials RR 0.96 (0.87 to 1.06)	Moderate
Trials with patient‐reported outcomes	0.93 (0.86 to 1.00)	4046 (31)	Symmetrical funnel plot Moderate heterogeneity	0.89 (0.72 to 1.11)	845 (4)	Substantial heterogeneity (see above).	Moderate
Trials with observer‐reported outcomes	0.93 (0.85 to 1.02)	1995 (13)	Symmetrical funnel plot Moderate heterogeneity	0.95 (0.77 to 1.17)	54 (1)	One small trial	Moderate