The purpose of this study is to assess safety and efficacy of empagliflozin compared to sitagliptin in patients with type 2 diabetes mellitus who are treatment-naive or on treatment with metformin and have insufficient glycaemic control. The study will assess non-inferiority of empagliflozin to sitagliptin with regards to HbA1c.

Inclusion criteria:

Inclusion criteria:

• Diagnosis of type 2 diabetes mellitus.
• Male and female patients on diet and exercise regimen who are:
• Treatment-naïve, defined as absence of any oral antidiabetic therapy for 12 weeks prior to randomisation.

or

• Pre-treated with immediate release metformin unchanged for 10 weeks prior to randomisation. Minimum dose for metformin: >=1500 mg/day or maximum tolerated dose or maximum dose according to local label.
• HbA1c of >= 7.5 % and <= 10.5 % at Visit 1 and 3.
• Age >= 18 yrs.

Exclusion criteria:

• Uncontrolled hyperglycaemia with a glucose level >270 mg/dL (>15 mmol/L) after an overnight fast during dose stabilisation (if applicable) and/or placebo run-in.
• Any other antidiabetic drug within 12 weeks prior to randomisation (applicable to treatment-naïve patients).
• Any other antidiabetic drug within 10 weeks prior to randomisation except metformin (applicable to patients on background treatment with metformin).
• Acute coronary syndrome (non-STEMI, STEMI and unstable angina pectoris), stroke or TIA within 3 months prior to informed consent.
• Indication of liver disease.
• Moderate to severe renal impairment.
• Bariatric surgery within the past two years.
• Treatment with anti-obesity drugs 3 months prior to informed consent.
• Current treatment with systemic steroids at time of informed consent or any other uncontrolled endocrine disorder except type 2 diabetes mellitus.