A Study of Oral Upadacitinib Tablets to Assess Change in Disease State in Participants Aged 12-75 Years With Moderate to Severe Atopic Dermatitis in Brazil

Inclusion Criteria: * Body weight \>= 40 kg at the Baseline Visit for participants between \>= 12 and \< 18 years of age. * Chronic Atopic Dermatitis (AD) with onset of symptoms at least 3 years prior to Baseline and participant meets Hanifin and Rajka criteria. * Eczema Area and Severity Index (EASI) score \>= 16 at the Screening and Baseline Visits. * Validated Investigator Global Assessment for AD (vIGA-AD) score ≥ 3 at the Screening and Baseline Visits. * \>= 10% body surface area of AD involvement at the Screening and Baseline Visits. * Worst Pruritus Numerical Rating Scale (NRS) ≥ 4 at Screening and Baseline Visits. * Documented history (within 1 year prior to the Screening Visit) of inadequate response (IR) to systemic methotrexate (MTX) and/or cyclosporin A (CsA) or not a candidate for systemic treatment with MTX or CsA as a result of intolerance or medical contraindication. Exclusion Criteria: * Prior exposure to any systemic Janus kinase (JAK) inhibitor. * Prior exposure to dupilumab. * Must not have used the following AD treatments within the specified timeframe prior to Baseline Visit: * Corticosteroids, MTX, CsA, azathioprine. phosphodiesterase type 4 (PDE4)-inhibitors, interferon-γ, and mycophenolate mofetil within 4 weeks. * Targeted biologic treatments (refer to within 5 half-lives \[if known\]) or within 12 weeks, whichever is longer. * Phototherapy treatment, laser therapy, tanning booth, or extended sun exposure that could affect disease severity or interfere with disease assessments within 4 weeks. * Oral or parenteral traditional medicine within 4 weeks. * Moisturizers that contain Topical corticosteroids (TCS), Topical calcineurin inhibitor (TCI)s, or topical Phosphodiesterase type 4 (PDE-4) inhibitors within 7 days.