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 glycated 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 maintain these changes subsequently 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 (DPP-4i), sodium-glucose cotransporter-2 inhibitor (SGLT2i), thiazolidinedione (TZD), glucagon-like peptide 1 receptor agonists (GLP-1 RAs), sulfonylurea (SU), α-glucosidase inhibitor (α-Gi), 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, cardiovascular benefit, risk of hypoglycemia, impact of body weight, 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), CV benefit (blue), hypoglycemia risk (red), and body weight changes (yellow) were assigned ratings of low, intermediate, or high (body weight changes; decrease, neutral, or increase) 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. This figure was illustrated based on the drugs' approval by the Korea Food and Drug Administration (http://www.mfds.go.kr/eng) in April 2019 [23]. GLN, glinide. ^aBody weight changes: decrease, neutral, or increase, ^bGLN can be used as dual combination therapy with metformin, TZD, α-Gi, or insulin or as a triple combination therapy with metformin and α-Gi, metformin and TZD, or metformin and insulin.