The main purpose of this study is to evaluate how much of the study drug (LY3871801), 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 male participants. The study will also measure how much of the study drug gets into the bloodstream, how its broken down, and how long it takes the body to get rid of it. The study will last up to approximately 9 weeks including the screening period.

Inclusion Criteria:

• Male participants who are overtly healthy as determined by medical evaluation
• Have a body mass index of 18.5 to 32.0 kilograms per meter squared (kg/m²), inclusive
• Males who agree to use highly effective or effective methods of contraception

Exclusion Criteria:

• Have known allergies to LY3871801, related compounds, or any components of the formulation, or a history of significant atopy
• Have received or intend to receive any vaccination within 30 days prior to dosing until the follow-up phone call
• Have participated in a radiolabeled drug study, where exposures are known to the investigator or designee, within 4 months prior to check-in, or participated in a radiolabeled drug study, where exposures are not known to the investigator or designee, within 6 months prior to check-in