Is transcutaneous auricular vagus nerve stimulation effective and safe for primary insomnia? A PRISMA-compliant protocol for a systematic review and meta-analysis

Background: Insomnia is a highly prevalent sleep disorder with substantial impacts on health and quality of life. Current treatment options have certain limitations, highlighting the need for novel therapeutic approaches. Transcutaneous auricular vagus nerve stimulation (ta-VNS) is gaining recognition as a promising non-invasive neuromodulation technique for treating insomnia, but its efficacy has not been systematically evaluated. Therefore, this protocol outlines the framework for a systematic review and meta-analysis designed to comprehensively assess the effectiveness and safety of ta-VNS in treating primary insomnia. Methods: A thorough literature search will be carried out in Embase, PubMed, the Cochrane Library, PsycINFO, AMED, PEDro, Wangfang database, Chinese National Knowledge Infrastructure, and Chinese BioMedical Literature Database, covering publications from their inception until December 31, 2024. Randomized controlled trials evaluating ta-VNS for primary insomnia in adults will be included. Two independent reviewers will screen studies, gather data, and evaluate the risk of bias based on the Cochrane RoB 2.0 tool. Meta-analyses will be conducted where appropriate, and the quality of evidence will be evaluated using GRADE. Subgroup and sensitivity analyses are planned. Discussion: This systematic review and meta-analysis will deliver a thorough synthesis of existing evidence regarding the efficacy and safety of ta-VNS for insomnia, potentially informing clinical practice and future research directions. Trial registration: PROSPERO registration number: CRD42024529039.