Background: The clinical management of major depressive disorder (MDD) is hampered by the lack of objective biomarkers and high inter-individual variability in drug response, with conventional antidepressants achieving only a 50% response rate.

Objective and Design: This prospective, randomized, parallel-controlled trial aims to enroll 220 MDD patients, who will be allocated 1:1 to either a pharmacogenomics (PGx)-guided therapy group (treatment selection based on genetic testing) or a conventional treatment group (treatment as usual per guidelines), with a 12-week follow-up. Additionally, a matched healthy control cohort will be included for cross-sectional biomarker comparisons.

Intervention and Outcomes: Patients in the PGx group undergo buccal swab testing for key genetic polymorphisms (e.g., CYP2D6, CYP2C19) to inform antidepressant type and dosage. The primary outcome is the 12-week response rate (≥50% reduction in HAMD-17 score from baseline). Secondary outcomes include remission rate, incidence of adverse drug reactions, and medication adjustment frequency.

Exploratory Aims: Multidimensional baseline data-including resting-state fMRI (VMHC), peripheral blood biomarkers (inflammatory cytokines, thyroid function, BDNF), urinary metabolites, and gut microbiome-will be integrated to construct a predictive model for treatment efficacy and to identify novel MDD biomarkers.

Scientific Significance: This study seeks to validate the clinical utility of PGx-guided prescribing and to advance the shift from symptom-based diagnosis towards a biological-characteristic-based precision medicine framework for depression.