Efficacy of transcranial alternating current stimulation for insomnia: a GRADE-assessed systematic review and meta-analysis of randomized controlled trials

Insomnia affects 10–30% of adults worldwide, with current treatment options showing limited efficacy. Transcranial alternating current stimulation (tACS) has emerged as a promising neuro-modulatory approach, though its clinical utility remains uncertain. We systematically reviewed and meta-analyzed randomized controlled trials (RCTs) comparing tACS with sham stimulation for adults with insomnia. Databases searched included PubMed, Embase, the Cochrane Library, and ClinicalTrials.gov (inception to July 2025). Primary outcomes were changes in Pittsburgh Sleep Quality Index (PSQI) and Insomnia Severity Index (ISI); secondary outcomes included sleep onset latency, sleep efficiency, mood symptoms (depression and anxiety), and total sleep time. Analysis of data was performed using random-effects model in RevMan (Version 5.4.1). Six RCTs with a total of 354 participants were included. Compared to sham, tACS significantly improved sleep quality, with a mean difference (MD) of − 2.99 in PSQI scores (95% CI: − 4.91 to − 1.06; p = 0.002; I2 = 90%), further supported by sensitivity analysis (MD: − 3.79; p < 0.00001; I2 = 22%). ISI improvements were not significant in the main analysis but became so in sensitivity analysis (MD: − 7.02; p < 0.00001). No significant effects were found for sleep latency, efficiency, total sleep time, and depression or anxiety scores. Although tACS shows potential for improving subjective sleep quality, it did not significantly improve objectively measured sleep efficiency. The high heterogeneity and predominance of low-certainty evidence limit confidence in these findings, and current evidence remains insufficient to support clinical recommendations. Further high-quality, large-scale RCTs are needed to optimize stimulation parameters and establish long-term efficacy.