This study includes two parts:
* Part 1: a randomized double-blind placebo-controlled induction period and
* Part 2: an extended treatment period for non-responders from Part 1.
In Part 1, participants will be randomized in a 2:1 ratio to upadacitinib 45 mg once daily (QD) or matching placebo for 12 weeks. The randomization will be stratified by baseline corticosteroid use (yes or no), endoscopic disease severity (Simplified Endoscopic Score for Crohn's disease \[SES-CD\] \< 15 and ≥ 15), and number of prior biologics with prior inadequate response or intolerance (0, 1, \> 1).
Participants who do not achieve clinical response at Week 12 will be able to enroll in Part 2 to receive a double-blind extended treatment with upadacitinib until Week 24. Clinical response is defined as a ≥ 30% decrease in average daily very soft or liquid stool frequency (SF) and/or ≥ 30% decrease in average daily abdominal pain (AP) score (both not worse than Baseline).
Participants who achieve clinical response at Week 12 may be eligible to enter the 52-week, double-blind, maintenance portion of Study M14-430 (NCT03345823).
