Alopecia Areata (AA) is a condition where the body's immune system attacks hair follicles, leading to hair loss. This study is testing a drug called upadacitinib to see if it's safe and effective for people with severe AA. Upadacitinib is already approved for other uses but is being tested here for AA. Participants will take either the drug or a placebo, which looks like the drug but has no active ingredients.

• The study could last up to 160 weeks, with visits to a hospital or clinic for check-ups.
• Participants may need to switch treatment groups at Weeks 24 and 52.
• Participants may experience a higher treatment burden than usual care.

To join, adults must be under 64, and in some cases, adolescents 12 and older can participate. Participants need to have had severe AA for less than 8 years, with no hair regrowth in the past 6 months. People with other types of hair loss or scalp issues cannot join. During the study, participants will have medical check-ups, blood tests, and answer questionnaires to see how the treatment is working.