This study is intended to assess the effect on HbA1c of different dose regimens of LX4211 in combination with metformin in subjects with Type 2 Diabetes Mellitus who have inadequate glycemic control on metformin monotherapy.

Inclusion Criteria:

• Adult subjects between the ages of 18 to 75 years, inclusive
• Confirmed diagnosis of Type 2 diabetes mellitus
• Meet required laboratory values at screening, including fasting plasma glucose less than 270 mg/dL
• Stable dose of metformin monotherapy greater than 1500 mg/day for at least 8 weeks
• Willing and able to provide written informed consent
• Willing and able to maintain consistent dietary, physical activity, and sleeping patterns throughout the study

Exclusion Criteria:

• History of Type 1 diabetes mellitus, diabetic ketoacidosis, hyperosmolar nonketotic syndrome, or diabetes resulting from pancreatic disorder or secondary diabetes
• History of renal disease or clinically significant abnormal kidney function tests
• Presence of active hepatic disease or clinically significant abnormal liver function tests
• Subjects with a history of heart attack, severe/unstable angina, or coronary revascularization procedure within 6 months prior to study Day 1
• History of clinically significant cardiac arrhythmias within one year of study Day 1
• Subjects with congestive heart failure
• Subjects with uncontrolled Stage III hypertension
• Triglycerides >1000 mg/dL at Screening
• Known history of HIV or hepatitis C
• History of illicit drug or alcohol abuse with one year of study Day 1
• Have had 2 or more emergency room visits, doctor visits, or hospitalizations due to hypoglycemia within 6 months of study Day 1
• Use of any other investigational drug within 30 days of study Day 1
• Prior exposure to LX4211
• Use of any medication or herbal supplement for the purpose of weight loss
• Chronic use of any antidiabetic therapy other than metformin in the 3 months prior to study Day 1
• Use of corticosteroids within 2 weeks prior to study Day 1
• Major surgery within 6 months of study Day 1
• Subjects with any history of severe gastroparesis
• Inability or difficulty swallowing whole capsules or tablets
• Women who are pregnant or breast feeding