Study of the Safety and Efficacy of MK-8521 Compared to Placebo and a Diabetes Drug in Participants With Type 2 Diabetes Mellitus (MK-8521-003)

Inclusion Criteria:

- Male, or female of non-childbearing potential with Type 2 diabetes mellitus

- Body mass index (BMI) between: 27 >= and <= 40 kg/m^2

- A1C (average blood sugar for the past 2 to 3 months) value >= 7.0 and <= 11.0 % at
the time of screening

- On a stable dose of metformin (>=1000 mg total daily dose) for at least 12 weeks at
the time of screening

Exclusion Criteria:

- Mentally or legally incapacitated

- History of clinically significant psychiatric disorder of the last 5 years.
Participants with situational depression may be enrolled in the trial at the
discretion of the Investigator

- History of Type 1 diabetes mellitus or a history of ketoacidosis

- History of clinically significant gastrointestinal, hematological, hepatic,
immunological, renal, respiratory, genitourinary or major neurological abnormalities
or diseases

- History of cardiovascular disease or cardiac conduction disorder

- History of cancer (malignancy). Exceptions may include adequately treated
non-melanomatous skin carcinoma or carcinoma in situ of the cervix or other
malignancies which have been successfully treated >=10 years prior to the
pre-screening visit

- History of proliferative diabetic retinopathy or maculopathy

- Clinically significant diabetic autonomic neuropathy

- QTc interval >= 470 msec (for males) or >= 480 msec (for females).

- Positive for hepatitis B surface antigen, hepatitis C antibodies, or human
immunodeficiency virus (HIV)

- On a weight loss program and is not weight-stable (weight stable is defined history
of <5% change in body weight in the last 3 months

- On a weight loss medication or has undergone bariatric surgery

- Major surgery, donated or lost 1 unit of blood (approximately 500 mL) within 4 weeks
prior to the pretrial (screening) visit

- Participated in another investigational trial within 4 weeks prior to the pretrial
(screening) visit

- History of acute or chronic pancreatitis of any etiology

- Mean value for triplicate semi-recumbent systolic blood pressure >160 mm Hg and/or
diastolic blood pressure >90 mm Hg (after at least a 5-minute seated rest) and blood
pressure is considered unlikely to be below these limits by Day-1 (Randomization)
with initiation or adjustment of antihypertensive medication

- Event of severe hypoglycemia with seizure or loss of consciousness in the past 12
months

- Treated with anti-hyperglycemic agents other than metformin within the last 12 weeks

- Previous exposure to any glucagon-like peptide-1 (GLP-1) receptor agonist (e.g.
Byetta™, Victoza™ or investigational agents)