Placebo Effect of Sham Acupuncture for Primary Insomnia: A Meta-Analysis of Randomised Controlled Trials

To provide updated evidence from randomised controlled trials (RCTs) on the placebo effect size and influencing factors of sham acupuncture for primary insomnia. A systematic literature review and meta-analysis were conducted in accordance with the PRISMA guidelines. Databases such as PubMed, Cochrane, Embase, Web of Science, China National Knowledge Infrastructure, Wanfang, China Science and Technology Journal Database and Chinese Biological Medicine Database were searched, focusing on sham acupuncture and primary insomnia. RCTs would be included if they compared the clinical efficacy of sham acupuncture before and after the intervention in patients with primary insomnia. The risk of bias of the included studies was evaluated using the Cochrane risk-of-bias tool (version 2.0). A total of 4348 studies were retrieved, and 36 eligible randomised controlled trials were included. The overall risk of bias in 13 studies were considered as high risk, 7 studies were categorised as some concerns and 16 studies were considered as low risk. The results of the meta-analysis showed that sham acupuncture significantly reduced Pittsburgh Sleep Quality Index (PSQI) [weighted mean difference (WMD) = 1.38, (95% confidence interval (CI) = 0.90, 1.86), p < 0.05] and Insomnia Severity Index (ISI) [WMD = 2.58, (95% CI = 1.46-3.69), p < 0.05]. There was no significant change in polysomnography and actigraphy. Sham acupuncture had a certain placebo effect in clinical trials of primary insomnia. The placebo effect varied from different types of sham acupuncture.