Effect of Add-on SGLT2i, TZD, or Combination Therapy in Type 2 Diabetes Patients on DPP4 Inhibitors

Inclusion Criteria: 1. Adults aged between 19 and 75 years at the time of providing written informed consent. 2. Diagnosed with type 2 diabetes mellitus and having an HbA1c level between 7.5% and 11.0%. 3. Receiving DPP4 inhibitor monotherapy or combination therapy with metformin and/or sulfonylurea for at least 8 weeks without dose adjustment. 4. Provided written informed consent voluntarily after receiving a full explanation of the study. 5. Considered capable of understanding the study procedures and cooperating throughout the study period until completion. Exclusion Criteria: 1. Patients with diabetes other than type 2 diabetes, including type 1 diabetes or gestational diabetes. 2. Use of TZD or SGLT2 inhibitors within the past 8 weeks, or history of discontinuation due to serious adverse reactions. 3. Currently receiving four or more antidiabetic medications. 4. History of diabetic ketoacidosis (with or without coma) or acute/chronic metabolic acidosis within the past 24 weeks. 5. Known allergy or hypersensitivity to the investigational drugs or their components. 6. Chronic use (more than 14 consecutive days) of oral or parenteral corticosteroids within 8 weeks prior to screening, with ongoing need for dose adjustment. 7. Genetic disorders such as galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption. 8. Active or progressive malignant tumors requiring treatment. 9. History of drug abuse or alcohol dependence within the past 12 weeks. 10. HIV infection. 11. Severe infections, perioperative status, or major trauma. 12. History of heart failure classified as NYHA class III or IV within the past 24 weeks. 13. History of acute cardiovascular events within the past 12 weeks (e.g., unstable angina, myocardial infarction, transient ischemic attack, stroke, coronary artery bypass grafting, or coronary intervention). 14. Renal failure or chronic kidney disease with eGFR \< 25 mL/min/1.73m² or undergoing dialysis. 15. Active bladder cancer or history of bladder cancer. 16. Abnormal liver function defined as serum ALT, AST, or alkaline phosphatase \> 5× ULN, or total bilirubin \> 5× ULN. 17. Pregnant or breastfeeding women. 18. Participation in another clinical trial or administration of investigational drugs within the past 12 weeks (except for observational or retrospective studies deemed not to affect the safety or efficacy of this trial). 19. Determined by the investigator to be unsuitable for participation in the study.