Despite the current guideline's recommendation of a timely stepwise intensification therapy, the "clinical inertia", termed as the delayed treatment intensification, commonly exists in the real world, which may be partly due to the relatively little substantial evidence and no clear consensus regarding the efficacy and safety of triple oral agents in patients inadequately controlled with dual therapy. In this clinical trial performed in 237 centers in China, 5,535 type 2 diabetic patients inadequately controlled by previous therapies were treated with a stable metformin/sitagliptin dual therapy for 20 weeks. The patients who did not reach the glycated hemoglobin A1c (HbA1c) goal were then further randomized into glimepiride, gliclazide, repaglinide, or acarbose group for an additional 24-week triple therapy. A mean HbA1c reduction of 0.85% was observed when sitagliptin was added to the patients inadequately controlled with metformin in 16 weeks. Further HbA1c reductions in the 24-week triple therapy stage were 0.65% in glimepiride group, 0.70% in gliclazide group, 0.61% in repaglinide group, and 0.45% in acarbose group. The non-inferiority criterion for primary hypotheses was met for gliclazide and repaglinide, but not for acarbose, compared with glimepiride, when added to metformin/sitagliptin dual therapy. The incidences of adverse events (AEs) were 29.2% in the dual therapy stage and 30.3% in the triple therapy stage. Metformin/ sitagliptin as baseline therapy, with the addition of a third oral antihyperglycemic agent, including glimepiride, gliclazide, repaglinide, or acarbose, was effective, safe and well-tolerated for achieving an HbA1c < 7.0% goal in type 2 diabetic patients inadequately controlled with previous therapies. The timely augmentation of up to three oral antihyperglycemic agents is valid and of important clinical benefit to prevent patients from exposure to unnecessarily prolonged hyperglycemia.