The purpose of this study is to evaluate how well LY3375880 (study drug) is tolerated in healthy participants and what side effects may occur. The study drug will be administered either subcutaneously (SC) under the skin or intravenously (IV) into a vein in the arm.

This is a two-part study. Participants will enroll in only one part. Part one will last about 16 weeks including screening and follow-up. This part will include 2 nights at the study site. Part two will last about 20 weeks including screening and follow-up. This part will include 2 nights at the study site for each dose.

Inclusion Criteria:

• Are overtly healthy males or females, as determined by medical history and physical examination
• Have a body mass index of 18.0 to 32.0 kilograms per meter squared (kg/m²) inclusive
• Are reliable and willing to make themselves available for the duration of the study and are willing to follow study procedures

Exclusion Criteria:

• Have known allergies to LY3375880, related compounds or any components of the formulation, or history of significant atopy
• Are women who are of childbearing potential or who are lactating