Purpose of the Review:

Transcranial alternating current stimulation (tACS) is a non-invasive technique that modulates brain oscillations and may help treat hallucinations when conventional treatments fail. This systematic review evaluated the efficacy of tACS in reducing hallucinations in psychiatric disorders.

Collection and Analysis of Data:

A systematic search of PubMed, Scopus, EMBASE, and clinical trial registries was conducted. Studies included adult psychiatric populations receiving tACS with hallucinations measured using standardized scales. Three randomized controlled trials (RCTs) were included in the meta-analysis, and five additional studies were synthesized qualitatively. Risk of bias was assessed using the Cochrane RoB 2 tool for RCTs, and the Joanna Briggs Institute tools for other designs, and certainty of evidence was assessed using GRADE.

Meta-analysis of three RCTs (72 participants) showed no significant difference between tACS and sham treatment in reducing hallucinations post-intervention (SMD = –0.14, 95% CI = –0.61 to 0.32) or at study endpoint (SMD = 0.10, 95% CI = –0.41 to 0.61). Qualitative findings suggested potential benefits with gamma-frequency (40 Hz) tACS for auditory hallucinations in schizophrenia. Side effects were mild and infrequent. Overall risk of bias was moderate to high, and evidence certainty was low.

Conclusions:

Gamma-frequency tACS shows potential, but evidence remains inconclusive. Larger, well-designed trials are needed to determine its effectiveness for hallucinations in psychiatric disorders. Persistent auditory hallucinations pose treatment challenges in schizophrenia. Non-invasive brain stimulation such as TMS and tDCS has been found to offer some benefit for auditory hallucinations. However, the literature on the efficacy of tACS for auditory hallucinations has not been reviewed. This systematic review has synthesized all published studies and reported the pooled effect for efficacy and safety.