This is a Phase 1 open-label study of the effect of itraconazole on the pharmacokinetics of CTP-543 in healthy subjects.

Inclusion Criteria:

• Non-smoker who has not used nicotine-containing products for at least 3 months prior to the first dosing and throughout the study
• Body mass index (BMI) ≥ 18.0 and ≤ 32.0 kg/m2 at Screening
• Medically healthy with no clinically significant medical history, physical examination, laboratory profiles, vital signs or ECGs
• If of reproductive age, willing and able to use a medically highly effective form of birth control 30 days prior to first dose, during the study and for 30 days following last dose of study medication.
• Understands the study procedures in the informed consent form, and be willing and able to comply with the protocol

Exclusion Criteria:

• History or presence of clinically significant medical or psychiatric condition or disease
• History of any illness that might confound the results of the study or poses an additional risk to the subject by their participation in the study
• History or presence of alcohol or drug abuse within the past 2 years prior to the first dosing
• Females who are nursing, pregnant, or planning to become pregnant while in the study, and for 30 days after last dose of study drug
• Positive results at Screening for human immunodeficiency virus (HIV), hepatitis B surface antigen (HBsAg) or hepatitis C virus (HCV)
• A positive test or history of incompletely treated or untreated tuberculosis
• Donation of > 499 mL of blood or plasma within 56 days of Screening (during a clinical trial or at a blood bank donation) and for 30 days after last dose of study drug