Background

Sham acupuncture is commonly used as a control in clinical acupuncture trials. However, its placebo effects remain unclear, and there is no standardized protocol regarding stimulation intensity or needling location.

Objective

Using randomized controlled trials (RCTs) of acupuncture for insomnia as an example, this study aimed to evaluate the placebo effect of sham acupuncture and to analyze how stimulation intensity and acupoint location influence this effect.

Search strategy

A comprehensive search was conducted in PubMed, Embase, Cochrane Central Register of Controlled Trials, China National Knowledge Infrastructure, Wanfang, and Chinese Scientific Journals Database from the inception until January 25, 2025.

Inclusion criteria

Eligible studies were RCTs involving participants diagnosed with insomnia or other sleep disorders that compared acupuncture to sham acupuncture. No restrictions were placed on disease duration or severity.

Data extraction and analysis

Primary outcome measures were Pittsburgh Sleep Quality Index (PSQI) and Insomnia Severity Index (ISI). Secondary outcomes included total sleep time, sleep efficiency, sleep awakening time, and PSQI scores at a 4-week follow-up. Studies reporting at least one primary outcome were eligible for inclusion. For continuous outcomes, mean difference (MD) with 95% confidence interval (CI) were calculated. When measurement units were inconsistent or outcome variability was high, standardized MD (SMD) and 95% CI were calculated. Pairwise meta-analyses were conducted using Review Manager 5.4, while network meta-analyses were performed using Stata 16. The risk of bias was assessed using the Cochrane risk of bias tool.

Results

A total of 15 RCTs involving 609 participants were included. Compared to baseline, sham acupuncture significantly improved PSQI scores (MD = 1.43; 95% CI: [0.91, 1.94]; P < 0.0001; I² = 61%) and sleep efficiency (MD = –2.53; 95% CI: [–4.77, –0.29]; P = 0.03; I² = 91%). Subgroup analysis revealed that low-intensity stimulation and medium-frequency treatment (13–20 sessions) were associated with stronger placebo effects. The network meta-analysis suggested a potential interaction between stimulation intensity and treatment location. Among all subgroups, sham acupuncture performed at non-meridian, non-acupoint locations using low-intensity stimulation produced the greatest placebo effects in terms of PSQI improvement, ISI reduction, and prolongation of sleep duration, achieving the highest value of surface under the cumulative ranking curve.

Conclusion

Sham acupuncture produces a measurable and relatively stable placebo effect in insomnia patients. The effectiveness varied across different sham protocols, with low-intensity stimulation and medium-frequency regimens (13–20 sessions) showing stronger placebo responses. According to the network meta-analysis, sham acupuncture with low-intensity stimulation at non-acupoints yielded the strongest placebo effect. These findings emphasize the critical role of the sham acupuncture modality and procedural design in shaping placebo responses. However, the predominance of single-blind trials, along with regional and cultural variations, may introduce performance bias and limit the generalizability of the results.

Key words: Sham acupuncture, Placebo, Insomnia, Systematic review