Study to Evaluate the Safety and Efficacy of CTP-543 in Adults With Moderate to Severe Alopecia Areata

Inclusion Criteria:

* Definitive diagnosis of alopecia areata with a current episode lasting at least 6 months and not exceeding 10 years at the time of Screening. Total disease duration greater than 10 years is permitted.
* At least 50% scalp hair loss, as defined by a Severity of Alopecia Tool (SALT) score ≥50, at Screening and Baseline.
* Clinical lab results within the normal range

Exclusion Criteria:

* Active scalp inflammation, psoriasis, or seborrheic dermatitis requiring topical treatment to the scalp, significant trauma to the scalp, or untreated actinic keratosis on the scalp.
* Treatment with systemic immunosuppressive medications or biologics.
* Vaccination with herpes zoster vaccine or any live virus within 6 weeks of screening or during the study