Fig. 1. Antihyperglycemic therapy algorithm for adult patients with type 2 diabetes mellitus (T2DM). The algorithm stratifies the choice of medications for T2DM based on initial glycosylated hemoglobin (HbA1c) levels and demonstrates drug arrangement in a centrifugal direction. This algorithm includes only U.S. Food and Drug Administration-approved classes of medications for T2DM that are prescribed in Korea. For newly diagnosed T2DM, begin with lifestyle modification (LSM) at the time of diagnosis and subsequently maintain these changes for the duration of treatment. The HbA1c target is <6.5%; if this is not achieved within 3 months after implementing LSM, then the use of an antihyperglycemic agent should be initiated promptly. If the HbA1c level is <7.5%, metformin monotherapy is the preferred choice for pharmacotherapy in conjunction with LSM. If there are contraindications for metformin or side effects, then consider other monotherapy options such as a dipeptidyl peptidase 4 inhibitor (DPP4i), sodium-glucose cotransporter 2 inhibitor (SGLT2i) thiazolidinedione (TZD), glucagon-like peptide 1 receptor agonists (GLP-1RAs), sulfonylurea (SU), α-glucosidase inhibitor (AGI), or insulin as the initial therapy according to the patient's condition. If the initial HbA1c level is <7.5% or the HbA1c target is not achieved within 3 months of monotherapy, dual combination therapy can be considered. In this case, a second-line drug is added to metformin; however, any other combination of drugs with different mechanisms of action can be used depending on the patient's clinical characteristics. If the HbA1c target is not achieved within 3 months after commencing dual therapy, then proceed to triple combination therapy. In no particular order of preference, efficacy, risk of hypoglycemia, weight gain, impact on cardiovascular (CV) outcomes, and presence of clinical data in the Korean population should be considered for this arrangement. To aid the physician's choice, the characteristics of antihyperglycemic agent classes are shown as a bar scale. Efficacy (green), hypoglycemia risk (red), body weight gain (yellow), and CV benefit (blue color) were assigned ratings of low, intermediate, or high based on recently published studies identified in an extensive literature review; the scale bar is not constructed according to strict definitions but should be used as a guide for clinical decisions. GLN, glinide (meglitinide). ^aGLN can be used as dual combination therapy with metformin, TZD, AGI, or insulin or as a triple combination therapy with metformin and AGI, metformin and TZD, or metformin and insulin.