Background: Photobiomodulation (PBM), also referred to as low-level light therapy (LLLT), is an emerging non-pharmacological approach. This treatment is considered low-risk, cost-effective, and non-invasive, utilizing near-infrared light (NIR). The purpose of this paper is to explore the underlying mechanism of action and conduct a systematic review of pre-clinical and clinical research on the use of PBM for psychiatric disorders. Methods: A search on the PubMed, Cochrane Library, and EMBASE databases was performed on 18 and 26 January 2024. Publications focused on PBM treatment in psychiatric disorders such as major depressive disorder, general anxiety disorder, dementia, Parkinson’s disease, traumatic brain injury, schizophrenia, and sexual disfunctions were included (n = 23). Results: Near-infrared stimulation is presented as an effective method, comparable to psychopharmacological treatment. The primary suggested mechanism for PBM is the stimulation of mitochondrial metabolism following the absorption of NIR energy by cytochrome C oxidase. Because of the method of implementation, which omits the liver metabolism of cytochrome P450, PMB is recognized as safe as it does not interact with other drugs. Limitations: Clinical studies vary in terms of population and treatment parameters, and most do not include a suitable control group. Conclusions: Preliminary results support the potential of NIR stimulation as a novel and innovative treatment for psychiatry. Further studies are needed to estimate the proper protocols of parameters singly for any disease.

The prevalence of auditory verbal hallucinations in schizophrenia is high, and many patients achieve no improvement despite adequate pharmacological treatment. This case report describes a 59-year-old female schizophrenia patient with chronic, treatment-refractory auditory verbal hallucinations. A total of 15 transcranial direct current stimulation procedures were administered over the left dorsolateral prefrontal cortex and left superior temporal gyrus. Following treatment, the patient achieved complete remission of auditory verbal hallucinations that lasted at least two weeks after the therapy was completed. Electroencephalogram-based analyses of power spectra and coherence are presented, demonstrating potential mechanisms that may underlie clinical effects of transcranial direct current stimulation in auditory verbal hallucinations.