Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by persistent synovial inflammation, progressive joint destruction, pain, and functional disability. Although conventional synthetic disease-modifying antirheumatic drugs (csDMARDs) are the standard treatment, many patients continue to have active disease despite therapy. Umbilical cord-derived mesenchymal stromal cell (UC-MSC) secretome contains bioactive molecules with immunomodulatory and anti-inflammatory properties that may improve clinical outcomes. This randomized, double-blind, placebo-controlled trial evaluates the efficacy and safety of intramuscular UC-MSC secretome as an adjunct to standard csDMARD therapy in patients with moderate rheumatoid arthritis. Clinical response, inflammatory biomarkers, and adverse events are evaluated throughout the study.