摘要Background:The use of inserted sham acupuncture as a placebo in randomized controlled trials(RCTs)is controversial,because it may produce specific effects that cause an underestimation of the effect of acupuncture treatment.Objective:This systematic survey investigates the magnitude of insert-specific effects of sham acupunc-ture and whether they affect the estimation of acupuncture treatment effects.Search strategy:PubMed,Embase and Cochrane Central Register of Controlled Trials were searched to identify acupuncture RCTs from their inception until December 2022.Inclusion criteria:RCTs that evaluated the effects of acupuncture compared to sham acupuncture and no treatment.Data extraction and analysis:The total effect measured for an acupuncture treatment group in RCTs were divided into three components,including the natural history and/or regression to the mean effect(con-trolled for no-treatment group),the placebo effect,and the specific effect of acupuncture.The first two constituted the contextual effect of acupuncture,which is mimicked by a sham acupuncture treatment group.The proportion of acupuncture total effect size was considered to be 1.The proportion of natural history and/or regression to the mean effect(PNE)and proportional contextual effect(PCE)of included RCTs were pooled using meta-analyses with a random-effect model.The proportion of acupuncture pla-cebo effect was the difference between PCE and PNE in RCTs with non-inserted sham acupuncture.The proportion of insert-specific effect of sham acupuncture(PIES)was obtained by subtracting the propor-tion of acupuncture placebo effect and PNE from PCE in RCTs with inserted sham acupuncture.The impact of PIES on the estimation of acupuncture's treatment effect was evaluated by quantifying the percentage of RCTs that the effect of outcome changed from no statistical difference to statistical differ-ence after removing PIES in the included studies,and the impact of PIES was externally validated in other acupuncture RCTs with an inserted sham acupuncture group that were not used to calculate PIES.Results:This analysis included 32 studies with 5492 patients.The overall PNE was 0.335(95％confidence interval[CI],0.255-0.415)and the PCE of acupuncture was 0.639(95％CI,0.567-0.710)of acupuncture's total effect.The proportional contribution of the placebo effect to acupuncture's total effect was 0.191,and the PIES was 0.189.When we modeled the exclusion of the insert-specific effect of sham acupunc-ture,the acupuncture treatment effect changed from no difference to a significant difference in 45.45％of the included RCTs,and in 40.91％of the external validated RCTs.Conclusion:The insert-specific effect of sham acupuncture in RCTs represents 18.90％of acupuncture's total effect and significantly affects the evaluation of the acupuncture treatment effect.More than 40％of RCTs that used inserted sham acupuncture would draw different conclusions if the PIES had been con-trolled for.Considering the impact of the insert-specific effect of sham acupuncture,caution should be taken when using inserted sham acupuncture placebos in RCTs.