This clinical trial studies the long-term effects of ritlecitinib in people with alopecia areata, a condition that causes hair loss. The study includes patients with severe forms of the disease, including alopecia totalis (complete loss of scalp hair) and alopecia universalis (loss of all body hair), who have previously participated in related studies.

The study uses ritlecitinib (also known as PF-06651600) in the form of hard capsules that are taken by mouth. Participants will receive either ritlecitinib at doses of 30 mg or 50 mg daily, or placebo. The treatment will continue for up to 36 months to evaluate how safe and effective the medication is over an extended period.

During the study, doctors will monitor hair growth on the scalp, eyebrows, and eyelashes. They will also track any changes in the participants’ quality of life, emotional well-being, and behavior. The main focus is on checking the safety of the treatment and measuring how well it works in managing hair loss caused by alopecia areata.