The main purpose of the trial is to determine the effect of a study drug known as LY2409021 on blood pressure and pulse rate in participants with type 2 diabetes mellitus (T2DM) when compared to placebo. The study has two periods. Each participant will receive LY2409021 or placebo in each period. At least 4 weeks will pass between periods. The study will last about 23 weeks for each participant. Participants may remain on stable dose metformin, as prescribed by their personal physician.

Inclusion Criteria:

• Have type 2 diabetes mellitus (according to the World Health Organization diagnostic criteria) and use diet and exercise alone or in combination with a stable dose of metformin ( >/=1000 mg/day [or <1000 mg, if documented intolerance to 1000 mg or higher dosages] immediate-release metformin or extended-release metformin for at least 2 months before screening).

• Have glycated hemoglobin (HbA1c) values >/=6.5% and </=8.5%, as determined by the central laboratory at screening.

• Have mean blood pressures >90/60 millimeters of mercury (mm Hg) and <140/90 mm Hg at screening.

• If being treated for hypertension, are taking 3 or fewer antihypertensive medications and have been taking stable doses of the same medications for at least 1 month before screening.

• Stable body weights (±5%) for >/=3 months before screening.

• Body mass indexes >/=20 kilograms/meters squared (kg/m²) and <40 kg/m².

• In the investigator's opinion, are well motivated, capable, and willing to:

  • Reliably administer the oral study drug once daily;
  • Maintain a study diary;
  • Perform self-monitored blood glucose testing; and
  • Wear an ambulatory blood pressure monitoring device for at least 24 hours (on multiple occasions).

• Are women not of child-bearing potential due to:

  • Surgical sterilization, hysterectomy, or bilateral oophorectomy (at least 6 weeks postsurgery) or tubal ligation (confirmed by medical history); or
  • Menopause. Women with an intact uterus are deemed menopausal if they have a cessation of menses for at least 1 year with follicle stimulating hormone >40 milli-international units per milliliter (mIU/mL), are not taking hormones or oral contraceptives within 1 year, and are otherwise healthy.

• Males who are sexually active and/or have partners of child-bearing age must use reliable methods of birth control during the study and until 3 months after the last doses of study medication. These requirements do not apply if a participant or his partner has been surgically sterilized or is not between menarche and 1 year postmenopausal.

Exclusion Criteria:

• Have severe gastrointestinal disease that may significantly affect gastric emptying or motility.
• Previous histories or active diagnoses of pancreatitis.
• Acute or chronic hepatitis, signs or symptoms of any other liver disease, or alanine aminotransferase (ALT) level greater than 2.5 times the upper limit of normal (ULN).
• Elevated total bilirubin (greater than 2 times ULN), clinically suspicious signs or symptoms of cirrhosis or history of cirrhosis.
• Mean resting pulse rate (PR) less than 60 beats per minute (bpm) or greater than 100 bpm.
• Current diagnosis or personal history of neuroendocrine tumors, family history of any type of multiple endocrine neoplasia, or Von Hippel-Lindau disease.