- Diagnosis of type 2 diabetes mellitus currently treated with metformin alone but, experiencing inadequate glycemic control. The participant should have received the metformin monotherapy for at least the 3 months prior to Screening; and must have a stable dose of greater than or equal to 1500 mg metformin for at least 8 weeks prior to randomization. Participants with a maximum tolerated dose that is documented to be less than 1500 mg of metformin may also be enrolled if this dose has been stable for 8 weeks prior to randomization.