Venlafaxine for Non-specific Low Back Pain

Inclusion Criteria: * Adults aged 18 to 75 years. * Diagnosis of chronic nonspecific low back pain, defined as pain located below the costal margin and above the inferior gluteal folds, lasting for more than 3 months, without a specific pathological cause. * Moderate to severe pain, defined as a Numerical Rating Scale score of 3 or higher. * Able to understand the study procedures and sign written informed consent. Exclusion Criteria: * Low back pain caused by a known specific pathological condition, including but not limited to fracture, malignancy, infection, inflammatory disease, or other identifiable structural or systemic causes. * Major comorbidities that may interfere with study outcomes or represent contraindications to the study medication. * Current or previous diagnosis of depression, regardless of whether treatment was received. * Current or previous use of antidepressant medication. * Current use of opioid analgesics. * Pregnancy, breastfeeding, or planned pregnancy during the study period. * Known allergy, hypersensitivity, or contraindication to toludesvenlafaxine. * History of psychosis or other major psychiatric disorders. * Any condition that, in the investigator's judgment, makes the participant unsuitable for the study.