A Preliminary Study of the Efficacy and Safety of MK-8521 for Type 2 Diabetes (MK-8521-004)

Inclusion Criteria: * Have T2DM in accordance with American Diabetes Association guidelines * Be on metformin monotherapy (\>-1000 mg/day: metformin IR or metformin XR) for at least 12 weeks prior to study start with a hemoglobin A1C (A1C) \>-7.5 and \<-10.5% OR Be on dual therapy with metformin (\>-1000 mg/day: dose stable for at least 4 weeks prior to study start) with an A1C of \>-7.0% and \<-10.0% and a second AHA and be willing to washout the second AHA. Allowable AHAs are dipeptidyl peptidase 4 (DPP-4 inhibitors), alpha-glucosidase inhibitors, sulfonylureas, and glinides. * Have a body mass index (BMI) ≥23 kg/m\^2 and ≤40 kg/m\^2 * Is a female who is not of reproductive potential, or is a female of reproductive potential who agrees to avoid becoming pregnant: while receiving study drug and for 14 days after the last dose of study drug Exclusion Criteria: * Have a history of type 1 diabetes or a history of diabetic ketoacidosis * Has a history of other specific types of diabetes (e.g., genetic syndromes, secondary pancreatic diabetes, diabetes due to endocrinopathies, drug- or chemical-induced, and post-organ transplant) * Has been treated with any gut-derived incretin hormone glucagon-like peptide 1 (GLP-1) receptor agonist (e.g. Byetta™, Victoza™ or investigational agents) within the last 6 months or has had GLP-1 receptor agonist discontinued due to gastrointestinal intolerance or lack of efficacy. Note: treatment with a GLP-1 receptor agonist that was discontinued \>6 months prior to study start is not an exclusion if the GLP-1 receptor agonist was discontinued for reasons other than gastrointestinal intolerance or lack of efficacy. * Has a history of clinically significant gastrointestinal disorder (including diabetic gastroparesis; irritable bowel disease; recurrent episodes of nausea, vomiting, diarrhea and abdominal pain) * Has a history of clinically significant and active, immunological, respiratory, genitourinary or major neurological (including stroke, transient ischemic attack and chronic seizures) abnormalities or diseases * Has a history of cardiovascular disease (including diabetic cardiomyopathy) or significant cardiac condition (including a history of myocardial infarction, stable or unstable angina, arterial revascularization, pathologic, symptomatic or sustained tachyarrhythmia \[e.g. atrial fibrillation, sustained supraventricular tachycardia, symptomatic non-sustained supraventricular tachycardia, ventricular tachycardia, ventricular fibrillation, Wolf-Parkinson-White syndrome, congenital long QT syndrome, etc.\]) or heart failure * Has a family history of medullary carcinoma of the thyroid or multiple endocrine neoplasm type-2 syndrome * Has active diabetic proliferative retinopathy or a history of maculopathy * Has human immunodeficiency virus (HIV) * Has a medical history of active liver disease (other than non-alcoholic hepatic steatosis), including chronic hepatitis B or C (assessed by medical history), primary biliary cirrhosis, or active symptomatic gallbladder disease * Is on a weight loss medication or has undergone bariatric surgery * Has a history of acute or chronic pancreatitis of any etiology * Had an event of severe hypoglycemia with neuroglycopenia in the past 12 months * Has a positive urine pregnancy test * Is pregnant or breast-feeding, or is planning to conceive during the trial, including 14 days following the last dose of investigational product * Routinely consumes \>1 alcoholic drinks per day or \>7 alcoholic drinks per week or engages in binge drinking * Routinely consumes ≥480mg /day caffeine in caffeinated beverages (1 cup of coffee contains approximately 120 mg of caffeine * Is taking a beta blocker or medications with sympathomimetic activity (e.g. pseudoephedrine, phenylpropanolamine, etc.) * Is currently a user of nicotine or nicotine containing products or does not agree to refrain from using nicotine during the trial, including 14 days following the last dose of investigational product * Is currently a user of any illicit drugs (including any marijuana use) or has a history of drug (including alcohol) abuse within approximately 5 years * has other severe acute or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation or blinded investigational product administration