The purpose of this study is to determine the effect of baricitinib on the levels of digoxin in the blood stream and how long it takes the body to remove digoxin. This study will also look at how safe and well-tolerated baricitinib is when given at the same time as digoxin in healthy participants. This study will last approximately 3-4 weeks.

Inclusion Criteria:

• Are overtly healthy males or females, as determined by medical history and physical examination
• Women not of child-bearing potential
• Menopausal women
• Have a body mass index of 18.0 to 29.0 kilograms per square meter (kg/m^2)

Exclusion Criteria:

• Women who are lactating
• Have previously completed or withdrawn from this study or any other study investigating baricitinib
• Currently enrolled in, have completed or discontinued within the last 90 days from a clinical trial involving an investigational product
• Have a pulse rate less than 50 beats per minute (bpm) at screening
• Have a current or recent history (less than 30 days prior to screening and/or less than 45 days prior to Day -1) of a clinically significant bacterial, fungal, parasitic, viral (not including rhinopharyngitis), or mycobacterial infection
• Have an absolute neutrophil count less than 2000 cells/microliter (2×10^9/liter) at screening or Day -1
• Show evidence of human immunodeficiency virus (HIV) infection and/or positive human HIV antibodies
• Have been exposed to a live vaccine within 12 weeks prior to the first dose or expected to need/receive a live vaccine
• Intend to use over-the-counter or prescription medication and/or herbal supplements within 14 days prior to dosing and during the study
• Have used or intend to use any drugs or substances that are known to be substrates, inducers, or inhibitors of P-glycoprotein (P-gp) within 30 days prior to dosing and throughout the study
• Have had symptomatic herpes zoster or herpes simplex infection within 90 days prior to the first dose

All enrolled participants.