The purpose of this study is to evaluate the effect of JTT-851 on diabetes as well as to assess the safety, tolerability, and pharmacokinetics of JTT-851 in type 2 diabetic patients either treated with metformin or treatment-naïve.

This is a randomized, double-blind, double-dummy, placebo and active-controlled (glimepiride), multi-center, parallel-group study to investigate the effect of JTT-851 on HbA1c and other ancillary efficacy parameters and to assess the safety, tolerability, and pharmacokinetics of JTT-851 in inadequately-controlled treatment-naïve or metformin-treated type 2 diabetic patients.

Inclusion Criteria:

• Males and females with type 2 diabetes, 18-70 years of age at Visit 1
• Managing diabetes with diet and exercise only or currently being treated with a stable dose of metformin (at least 1500 mg/day)
• Glycosylated hemoglobin at Visit 1 between 7.5% and 10.0%, if on metformin and between 7.5% and 10.9%, if without treatment
• Body mass index (BMI) ≥ 23.0 kg/m^2 and ≤ 45.0 kg/m^2 at Visit 1

Exclusion Criteria:

• Females who are pregnant or breast-feeding
• Known medical history or presence of type 1 diabetes or acute metabolic diabetic complications, unstable or rapidly progressing retinopathy, nephropathy or neuropathy
• Acute coronary syndrome or uncontrolled hypertension
• Does not meet all diet or previous/concomitant medication restriction criteria