The main purpose of this study is to evaluate how much of the study drug (LY3866288), administered as a single dose that has the radioactive substance 14C incorporated into it, passes from blood into urine, feces and expired air in healthy participants. The study will also measure how much of the study drug gets into the bloodstream when taken orally, compared to when injected directly into the vein, how its broken down, and how long it takes the body to get rid of it. The study will also evaluate the safety and tolerability of LY3866288.The study is conducted in two parts. The study is expected to last approximately 68 days.

Inclusion Criteria:

• Male and female participants who are overtly healthy determined by medical history, physical examination, 12-lead ECGs, vital signs measurements, and clinical laboratory evaluations at screening and/or check-in by the investigator
• Have Body mass index between 18.0 and 32.0 kg/m^2 (kilograms per meter squared)
• Male participants who are infertile via bilateral orchiectomy or vasectomy
• Female participants (non-childbearing potential only for Part A) who follow standard contraceptive methods

Exclusion Criteria:

• Female participants who are lactating or pregnant
• Have history of alcohol and/or drug abuse within 2 years prior to screening
• Have history or presence of any diseases or conditions of clinical significance by the Investigator (or designee) and/or Sponsor
• Have history of significant hypersensitivity, intolerance, or allergy to any drug compound, food, or other substance, unless approved by the investigator