Transcranial alternating current stimulation for chronic insomnia: a meta-analytic evaluation of sleep restoration and safety in adults

BACKGROUND: Chronic insomnia affects approximately one-third of adults globally, imposing substantial health burdens with limited effective treatments. Transcranial alternating current stimulation (tACS) emerges as a non-invasive neuromodulatory approach, though its efficacy and safety profile require systematic evaluation. METHODS: We systematically searched PubMed, Scopus, Web of Science, and Cochrane Central Register of Controlled Trials through July 2025 for randomized controlled trials (RCTs) evaluating tACS in adults with chronic insomnia. Primary outcomes included Pittsburgh Sleep Quality Index (PSQI) scores, sleep onset latency (SOL), total sleep time (TST), and subjective sleep efficiency. Secondary outcomes encompassed remission/response rates, daytime disturbances, mood symptoms, and adverse events. Data were pooled using random-effects models. Risk of bias and evidence certainty were assessed via Cochrane RoB 2.0 and GRADE. RESULTS: Four RCTs (n = 247) were included. tACS significantly reduced SOL at 2 weeks (MD = −56.90 min; 95% CI: −74.44 to −39.36) and 4 weeks (MD = −52.20 min; −67.03 to −37.37), improved PSQI (MD = −5.73; −8.35 to −3.10; p < 0.0001), increased TST (MD = +85.29 min; 33.42 to 137.15; p = 0.0013), and reduced daytime disturbances (MD = −0.94; −1.13 to −0.76; p < 0.0001). Response rates favored tACS (RR = 11.21; 3.20–39.23; p = 0.0002). Mood improvements were not sustained beyond 8 weeks. No significant adverse events emerged versus sham (RR = 1.06; 0.16–6.95). Heterogeneity ranged moderate-to-high (I2 = 46.9–97.2%). CONCLUSION: tACS demonstrates rapid efficacy (2–6 weeks) and safety for core insomnia symptoms. Sustained benefits require protocol optimization and long-term evaluation.