Objective
To systematically synthesize evidence on the psychobiological effects of music therapy and structured musical interventions on biomarkers in individuals with mental disorders, within a psychoneuroimmunological framework.

Methods
This systematic review and meta-analysis followed PRISMA 2020 guidelines. Searches were performed in PubMed, LILACS, PsycINFO, and Cochrane Library up to October 2025. Studies with individuals aged ≥16 years, psychiatric diagnoses, and both psychological and biomarker outcomes were eligible. Ten studies met inclusion criteria. Random-effects meta-analysis was conducted for sufficient, comparable data.

Results
Cortisol was the only biomarker with sufficient data for meta-analysis (n=4). Results showed no significant effect on cortisol levels (SMD = -0.18; 95% CI = -0.96 to 0.59), with substantial heterogeneity (I² = 88.7%). Exploratory analyses indicated more consistent responses in autonomic and inflammatory biomarkers than endocrine markers. Psychological outcomes showed greater improvement consistency across studies, even without short-term physiological changes. Findings must be interpreted cautiously due to the limited number of studies and high heterogeneity.

Conclusion
Psychobiological effects of music therapy and musical interventions vary by intervention, design, and population. Despite heterogeneity and limited quantitative data, findings support the clinical relevance of these interventions. More standardized, biomarker-informed research is needed to clarify underlying mechanisms.