A Study Evaluating the Efficacy and Safety of Oral Etrasimod in the Treatment of Adult Participants With Moderately to Severely Active Crohn's Disease

This study includes 5 substudies: Substudy A - Phase 2: A Phase 2, randomized, double-blind, substudy to assess the safety, tolerability, and efficacy of oral etrasimod therapy in participants with moderate to severe CD that supports the selection of an induction and maintenance dose(s) for Phase 3. Substudy 1 - Phase 2: A Phase 2b randomized, double-blind, placebo-controlled, dose-ranging induction substudy to evaluate etrasimod as induction therapy and select an induction and maintenance dose(s) for continued evaluation in Phase 3. Substudy 2 - Induction: A Phase 3 randomized, double-blind, placebo-controlled substudy to evaluate etrasimod as induction therapy. Substudy 3 - Maintenance: A Phase 3 randomized, double-blind, placebo-controlled substudy to evaluate etrasimod as maintenance therapy. Participants from Substudy 1 and Substudy 2 will be enrolled in Substudy 3. Substudy 4 - Long-Term Extension: A long-term extension substudy for participants who complete at least 52 weeks of treatment. Participants from Substudy 3 and Substudy A are planned to be enrolled in Substudy 4.