The gut-brain axis represents a complex communication network between the gastrointestinal tract and the central nervous system, influencing various aspects of mental health. This review explores the physiological mechanisms underlying this interaction, focusing on neurotransmitter production, immune system interactions, and microbial metabolites. Evidence suggests that dysbiosis, or imbalances in gut microbiota, can significantly impact mental health disorders such as depression, anxiety, and autism spectrum disorders. Mechanisms of gut-brain signaling include the vagus nerve, gut-derived neurotransmitters, and the blood-brain barrier. This review also examines experimental models and clinical studies that highlight the therapeutic potential of modulating gut microbiota through probiotics, prebiotics, and dietary interventions. Despite promising findings, challenges such as variability in research results and methodological limitations persist. Future research directions include exploring personalized medicine approaches and advancing technologies to deepen our understanding of the gut-brain axis.