The main purpose of this study is to evaluate how well LY4178256 is tolerated and what side effects may occur in healthy participants. Blood tests will be performed to check how much LY4178256 gets into the bloodstream and how long it takes the body to eliminate it. For each participant, the study will last about 7 months and will include either 7 or 12 visits depending on the assigned treatment.

Inclusion Criteria:

• Are overtly healthy as determined by medical evaluation including medical history, physical examination, and other screening procedures.
• Have a body mass index within the range of 19.0 to 32.0 kilograms per square meter (kg/m²)
• Individuals assigned male at birth willing to practice effective contraception throughout the study and individuals assigned female at birth not of childbearing potential may participate in this trial.

Exclusion Criteria:

• Have significant history of or current cardiovascular, respiratory, renal, gastrointestinal, endocrine, hematological, dermatological, or neurological disorders capable of significantly altering the absorption, metabolism, or elimination of drugs; of constituting a risk when taking the Investigational Medicinal Product (IMP); or of interfering with the interpretation of data.
• Have abnormal blood pressure
• Have a 12-lead electrocardiogram (ECG) abnormality at screening that, in the opinion of the investigator, increases the risks associated with participating in the study, have a mean QT interval corrected using Fridericia's formula (QTcF) of greater than 450 milliseconds (>450 msec) for males, or >470 msec for females.
• Regularly use known drugs of abuse or with positive drug results (within the past 3 months).
• Have a positive ethanol breath/urine test result or positive urine drugs of abuse screen at screening or check-in.
• Have hemoglobin level less than 12 grams per deciliter (<12 g/dL), or evidence of iron deficiency (ferritin less than 30 nanograms per milliliter (<30 ng/mL), or history or presence of hemoglobinopathy, or history hemolytic anemia. Participants who received transfusion within the past 12 weeks, or requiring regular transfusion should be excluded.
• Have clinically significant abnormal liver function tests at screening: alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphate (ALP), or total bilirubin ≥1.5x upper limit normal (ULN). Participants with confirmed Gilbert's syndrome may be enrolled.
• Have significant renal impairment (estimated glomerular filtration rate less than 60 milliliters per minute per square meter (eGFR<60mL/min/1.73 m ²)).