The purpose of this study is to examine the effect of gemfibrozil, ketoconazole, and clarithromycin on how much LY2409021 is found in the bloodstream and how long the body takes to get rid of it. The study is split into two parts, Part A and Part B. Participants in Part A are divided into two cohorts (groups). Each cohort will participate in two study periods. Period 1 involves a single dose of LY2409021. Period 2 involves either gemfibrozil or ketoconazole given daily for 21 days with LY2409021 given once on Day 4. Part A will last for 51 days and will also involve screening within 27 days of the start of the study. Part B is only open to participants who successfully completed Part A of the study. Participants in Part B will receive clarithromycin given daily for 21 days with LY2409021 given once on Day 4. Part B will last for 29 days and will also involve screening within 27 days of the start of the study.

Part B was added to the trial in August 2013, per protocol amendment.

Inclusion Criteria:

• Participants are overtly healthy males or females, as determined by medical history and physical examination
• Participants have a body mass index (BMI) of 18.0 to 32.0 kilograms per meter squared (kg/m^2), inclusive, at screening
• Participants have a fasting blood glucose of 54 to 110 milligrams per deciliter (mg/dL) (3.0 to 6.1 micromoles per liter [mmol/L])

Exclusion Criteria:

• Participants that have a contraindication to use of clarithromycin
• Participants that have a personal or family history of long QT syndrome
• Participants with a family history of sudden unexplained death or cardiac death in an immediate family member under 60 years of age
• Participants with a personal history of unexplained syncope within the last year
• Participants who have taken drugs or substances known to be an inducer or inhibitor of cytochrome P450 (CYP)3A4 or CYP2C8 or CYP2J2 (for example, St. John's wort, rifampin, ketoconazole, trimethoprim) within 30 days prior to the first dose

All participants enrolled in the study.