A Study Comparing Upadacitinib (ABT-494) to Placebo and to Adalimumab in Adults With Rheumatoid Arthritis Who Are on a Stable Dose of Methotrexate and Who Have an Inadequate Response to Methotrexate

This study consists of a 48-week double-blind treatment period (Period 1) and a long-term extension period (Period 2). Period 1 is a 48-week randomized, double-blind, parallel-group, placebo-controlled and active comparator-controlled period designed to compare the safety and efficacy of upadacitinib versus placebo, and versus adalimumab. Participants will be randomized in a 2:2:1 ratio to one of three treatment groups: * Placebo (up to Week 26) * Upadacitinib 15 mg once daily (QD) * Adalimumab 40 mg every other week (eow) Participants randomized to placebo who do not achieve a ≥ 20% improvement in tender joint count (TJC) and swollen joint count (SJC) at Weeks 14, 18, or 22 compared to Baseline will be switched to blinded upadacitinib treatment. At Week 26, all participants still receiving placebo will be switched to blinded upadacitinib treatment regardless of clinical response. Participants randomized to adalimumab who do not achieve a ≥ 20% improvement in TJC and SJC at Weeks 14, 18, or 22 compared to Baseline will be switched to blinded upadacitinib. Participants still receiving adalimumab at Week 26 who do not achieve low disease activity (LDA) according to Clinical Disease Activity Index (CDAI; LDA is defined as CDAI ≤ 10) will be switched to blinded upadacitinib treatment to Week 48. Participants randomized to upadacitinib who do not achieve a ≥ 20% improvement in TJC and SJC at Weeks 14, 18, or 22 compared to Baseline will be switched to blinded adalimumab; participants still receiving upadacitinib at Week 26 who do not achieve LDA (CDAI ≤ 10) will be switched to blinded adalimumab treatment to Week 48. Participants who complete the Week 48 visit (end of Period 1) will enter the long-term extension phase of the study (Period 2), for up to 5 years. Participants will continue study treatment as assigned at the end of Period 1. Starting at the Week 48 and thereafter, at least 20% improvement in both TJC and SJC compared to Baseline is required to remain on study drug. Anyone who does not fulfill this criterion at 2 consecutive visits (starting at Week 48) will be discontinued.