After baseline data are collected, eligible subjects will be randomized into each group at a 2:1 ratio (40 for repaglinide and 20 for metformin). IVGTT and hyperinsulinemic-euglycemic clamp will be done to 20 patients in repaglinide group and 10 patients in metformin group (less than 20% drop-off rate is acceptable for this study). Follow that, all patients will start to receive either repaglinide thrice daily (immediately before breakfast lunch, and dinner) or metformin thrice daily (after breakfast, lunch and dinner). The initial repaglinide doses will be based on HbA1c levels on the day of randomization (0.5 mg tid for HbA1c < 8% and 1 mg tid for HbA1c ≥ 8%); the initial dosage for metformin will be 0.5 g tid and this dosage will be kept until the end of this study.