This study is a randomized, double-blind, placebo-controlled, parallel-group study designed to evaluate the efficacy, safety, and tolerability of treatment with SEP-4199 CR at fixed doses of 200 mg/day or 400 mg/day compared with placebo for the treatment of major depressive episode associated with bipolar I disorder (bipolar I depression). The study is projected to randomize approximately 522 subjects inNorth America, Japan, Europe and Latin America, to SEP-4199 CR 200 mg/day, SEP-4199 CR 400 mg/day, and placebo treatment groups in a 1:1:1 ratio