A Study to Compare Upadacitinib (ABT-494) Monotherapy to Methotrexate (MTX) Monotherapy in Adults With Rheumatoid Arthritis (RA) Who Have Not Previously Taken Methotrexate

This study includes 2 periods (a 48-week double-blind treatment period and a long-term extension period) and a Japan substudy. In Period 1 participants will be randomized in a 1:1:1 ratio to treatment Groups 2, 3, and 4 below, except for participants from Japan, who will be randomized in a 2:1:1:1 ratio to Groups 1, 2, 3, and 4: * Group 1: Upadacitinib 7.5 mg once daily (QD) monotherapy (participants in Japan only) * Group 2: Upadacitinib 15 mg QD monotherapy * Group 3: Upadacitinib 30 mg QD monotherapy * Group 4: Methotrexate monotherapy Rescue therapy is defined for Weeks 12 through 24, Week 26, and Weeks 36 through 40. Starting at Week 12 through Week 24, participants who do not achieve ≥ 20% improvement in both tender joint count (TJC) and swollen joint count (SJC) compared with baseline at two consecutive visits will continue on their blinded therapy and the Investigator should optimize (initiate or increase) background RA medications: non-steroidal anti-inflammatory drug(s) (NSAIDs), corticosteroids (oral ≤ 10 mg/day prednisone equivalent or prednisone equivalent ≤ 0.5 mg/kg/day for 3 consecutive days) and/or low-potency analgesics. Rescue therapy for participants who meet the following criteria at Week 26 are as follows: Participants who do not achieve clinical remission (CR) based on Clinical Disease Activity Index (CDAI) (defined as a CDAI score ≤ 2.8): * but achieve ≥ 20% improvement in both TJC and SJC compared with baseline will continue on blinded study drug and the Investigator should optimize (initiate or increase) background RA medications: NSAIDs, corticosteroids (oral ≤ 10 mg/day prednisone equivalent and up to 2 local injections), low-potency analgesics and conventional synthetic disease-modifying anti-rheumatic drug(s) (csDMARDs) (only 1 of the following: sulfasalazine, hydroxychloroquine or chloroquine) throughout the remainder of Period 1 and until the study is unblinded. * and do not achieve ≥ 20% improvement in both TJC and SJC compared with baseline and originally assigned to methotrexate will be re-randomized in a 1:1 ratio to receive blinded upadacitinib 15 mg QD or upadacitinib 30 mg QD (participants in Japan will be randomized 1:1:1 to receive upadacitinib 7.5 mg QD, 15 mg QD, or 30 mg QD) while continuing methotrexate treatment in a blinded manner until the study is unblinded. Participants originally assigned to upadacitinib will add methotrexate 10 mg/week (7.5 mg for Japan) to upadacitinib in a blinded manner and will remain on upadacitinib plus methotrexate 10 mg/week (7.5 mg for Japan) until the study is unblinded. Starting at Week 36 through Week 40, participants who do not achieve ≥ 20% improvement in both TJC and SJC compared with baseline at two consecutive visits will continue on their blinded therapy and the Investigator should optimize (initiate or increase) background RA medications: NSAIDs, corticosteroids (oral ≤ 10 mg/day prednisone equivalent or prednisone equivalent ≤ 0.5 mg/kg/day for 3 consecutive days and up to 2 local injections), low-potency analgesics and csDMARDs (only 1 of the following: sulfasalazine, hydroxychloroquine or chloroquine). Participants who complete the Week 48 visit (end of Period 1) will enter the long-term extension, Period 2 (212 weeks) and continue study treatment per assignment at the end of Period 1 in a blinded fashion. When the last participant completes the last visit of Period 1 (Week 48), study drug assignment in both periods may be unblinded, and participants will be dispensed study drug in an open-label fashion until the completion of Period 2. Starting with Protocol Amendment 6, participants receiving upadacitinib 15 mg and 30 mg QD will receive open-label upadacitinib 15 mg QD, and participants receiving methotrexate will receive open-label methotrexate. A global analysis will be conducted for the comparisons of the primary and secondary efficacy endpoints between the upadacitinib 15 mg QD and 30 mg QD treatment groups versus the methotrexate treatment group for all participants (excluding the Japan specific upadacitinib 7.5 mg treatment group). Analyses will be conducted separately for United States (US)/Food and Drug Administration (FDA), European Union (EU)/European Medicines Agency (EMA), and Japan/Pharmaceuticals and Medical Devices Agency (PMDA) regulatory purposes, each according to a pre-specified sequence of primary and ranked secondary endpoints. A separate Japan sub-study analysis will be conducted for the comparisons of the efficacy endpoints between the upadacitinib 7.5 mg QD, 15 mg QD, and 30 mg QD treatment groups versus the methotrexate treatment group for participants enrolled in Japan only.