Evaluation of Upadacitinib in Adolescent and Adult Patients With Moderate to Severe Atopic Dermatitis (Eczema)

* Body weight of ≥ 40 kg at Baseline Visit for participants between ≥ 12 and \< 18 years of age * Chronic atopic dermatitis (AD) with onset of symptoms at least 3 years before Baseline Visit and subject meets Hanifin and Rajka criteria. * Active moderate to severe AD defined by: * Eczema Area and Severity Index (EASI) score ≥ 16 at the Screening and Baseline Visits; * Validated Investigator's Global Assessment (vIGA) score ≥ 3 at the Screening and Baseline Visits; * ≥ 10% Body surface area (BSA) of AD involvement at the Screening and Baseline Visits; * Baseline weekly average of daily Worst Pruritus NRS ≥ 4. * Candidate for systemic therapy or have recently required systemic therapy for AD * Subject has applied a topical emollient (moisturizer) twice daily for at least 7 days before the Baseline Visit. * Documented history of inadequate response to topical corticosteroids (TCS) or topical calcineurin inhibitor (TCI) or documented systemic treatment for AD within 6 months before Baseline Visit

* Prior exposure to any Janus kinase (JAK) inhibitor * Unable or unwilling to discontinue current atopic dermatitis treatments prior to the study * Requirement of prohibited medications during the study * Other active skin diseases or skin infections requiring systemic treatment or would interfere with appropriate assessment of atopic dermatitis lesions * Female subject who is pregnant, breastfeeding, or considering pregnancy during the study