Abstract: Objective · To investigate the clinical efficacy and degree of impact of placebo in the patients with primary insomnia. Methods · Databases including PubMed, Cochrane, and Embase were searched. The Consolidated Standards of Reporting Trials (CONSORT) was used as a reference standard for enrollment and evaluation. The objective and subjective sleep assessment indicators were collected before and after placebo treatment. Meta-analysis was performed using RevMan 5.3 and Comprehensive Meta-Analysis V2 softwares. Results · A total of 17 articles (18 studies) were included in the systematic review, and the total sample size was 1 980. These indicators were analyzedage subgroups (adults and elderly adults). The objective indicators showed that the number of awaking was only statistically different in elderly adults group (P0.043), while the latency period of sleep, wakefulness time after sleep onset and total sleep time were statistically different in both groups (P-0.414. Subjective indicators showed that the subjective total sleep time, subjective wakefulness time after sleep onset, and subjective number of awaking were statistically different in both groups (PP0.000). The absolute value of total effect range was 0.289-0.474. Conclusion · Placebo in the patients with primary insomnia can improve objective and subjective sleep assessment indicators, but the effect is small.

Key words: placebo, primary insomnia, meta-analysis, randomized controlled trial