24-week Study Comparing Lixisenatide to Sitagliptin as add-on to Metformin in Obese Type 2 Diabetic Patients Younger Than 50 Years

Inclusion criteria * Type 2 diabetes mellitus, diagnosed for at least 1 year at the time of screening visit, insufficiently controlled with metformin at a stable dose of at least 1.5 gram/day (g/day) for at least 3 months prior to the screening visit * Patients with obesity (BMI greater than equal to \[\>=\] 30 kg/m\^2) and aged from 18 years to less than 50 years Exclusion criteria * HbA1c less than (\<) 7.0 percent (%) or HbA1c greater than (\>) 10% at screening * Type 1 diabetes mellitus * Pregnant or breastfeeding women or women of childbearing potential with no effective contraceptive method * FPG at screening \>250 milligram/deciliter (mg/dL) (\>13.9 millimole/ liter \[mmol/L\]) * Weight change of more than 5 kg during the 3 months preceding the screening visit * History of unexplained pancreatitis, chronic pancreatitis, pancreatectomy, stomach/gastric surgery, inflammatory bowel disease, personal or family history of medullary thyroid cancer (MTC) or genetic conditions that predispose to MTC (for example, multiple endocrine neoplasia syndromes) * History of metabolic acidosis, including diabetic ketoacidosis within 1 year prior to screening * Hemoglobinopathy or hemolytic anemia or receipt of blood or plasma products within 3 months prior to the time of screening * Within the last 6 months prior to screening: history of myocardial infarction, stroke, or heart failure requiring hospitalization * Known history of drug or alcohol abuse within 6 months prior to the time of screening * Any clinically significant abnormality identified on physical examination, laboratory tests, electrocardiogram (ECG) or vital signs at the time of screening that in the judgment of the investigator or any sub-investigator could have precludes safe completion of the study or constrains efficacy assessment such as major systemic diseases, presence of clinically significant diabetic retinopathy or presence of macular edema likely to require laser treatment within the study period * Uncontrolled or inadequately controlled hypertension at the time of screening with a resting systolic or diastolic blood pressure \>180 millimeter of mercury (mmHg) or \>110 mmHg, respectively * Laboratory findings at the time of screening : Amylase and/or lipase \>3 times the upper limit of normal (ULN) laboratory range; alanine aminotransferase (ALT): \>3 times ULN; total bilirubin: \>1.5 times ULN (except in case of Gilbert's syndrome); hemoglobin \<11 gram/deciliter and/or neutrophils \<1500 per cubic millimeter (mm\^3) and/or platelets \<100 000/mm\^3; positive test for Hepatitis B surface antigen (HBsAg) and/or Hepatitis C antibody (HCAb), positive serum pregnancy test in females of childbearing potential, and calcitonin \>=20 picogram per milliliter (pg/mL) (5.9 picomole per liter) * Patients who are considered by the investigator or any sub-investigator as inappropriate for the study for any reason (for example, impossibility to meet specific protocol requirements \[such as scheduled visits, being able to do self-injections\], likelihood of requiring treatment during the screening phase and treatment phase with drugs not permitted by the clinical study protocol, investigator or any sub-investigator, pharmacist, study coordinator, other study staff or relative thereof directly involved in the conduct of the protocol) * Use of other oral or injectable antidiabetic or hypoglycemic agents than metformin (for example, sulfonylurea, alpha glucosidase inhibitor, thiazolidinedione, exenatide, dipeptidyl peptidase IV (DPP-IV) inhibitors, insulin) within 3 months prior to the time of screening * History of bariatric surgery, anti-obesity treatment, or unstable diet within 3 months prior to the time of screening * Use of systemic glucocorticoids (excluding topical application or inhaled forms) for one week or more within 3 months prior to the time of screening * Use of any investigational drug within 3 months prior to screening * Clinically relevant history of gastrointestinal disease associated with prolonged nausea and vomiting, including (but not limited to): gastroparesis, unstable (that is, worsening) and not controlled (that is, prolonged nausea and vomiting) gastroesophageal reflux disease requiring medical treatment, within 6 months prior to the time of screening * Any previous treatment with lixisenatide (for example, participation in a previous study with lixisenatide) * Allergic reaction to any glucagon like peptide-1 (GLP 1) agonist in the past (for example, exenatide, liraglutide) or to metacresol * History of a serious hypersensitivity reaction to sitagliptin * Moderate or severe renal impairment (creatinine clearance inferior to 50 milliliter/minute \[mL/min\]) * Additional exclusion criteria at the end of the run-in phase: informed consent withdrawal; lack of compliance during the single-blind placebo run-in period (\>2 injections missed or \>2 capsules missed); and patient with any adverse event which could have precludes the inclusion in the study, as assessed by the investigator