This clinical trial is focused on studying the condition known as Alopecia Areata, which is a type of hair loss that can affect the scalp and other parts of the body. The study will evaluate the safety and effectiveness of a medication called Upadacitinib, which is taken as a modified-release tablet. This means the tablet is designed to release the medication slowly over time. The study will compare the effects of taking Upadacitinib at different doses to a placebo, which is a tablet that does not contain the active medication.

The purpose of the study is to assess how well Upadacitinib works in reducing the signs and symptoms of severe Alopecia Areata in both adults and adolescents. Participants will be randomly assigned to receive either Upadacitinib or a placebo. The study will be conducted in several phases. Initially, participants will take the medication or placebo for a period of 24 weeks. After this period, some participants may continue in an extended phase of the study for up to 160 weeks, where the long-term effects and safety of the medication will be further evaluated.

Throughout the study, participants will be monitored to see how their condition responds to the treatment. The main goal is to determine if Upadacitinib can help reduce hair loss and improve hair regrowth in those with severe Alopecia Areata. The study will also look at the safety of the medication and how well it is tolerated by participants over time. This research aims to provide valuable information on the potential benefits of Upadacitinib for individuals affected by this condition.