This is a Phase 3, randomized, double-blind, placebo-controlled, multicenter, inpatient study in participants with bipolar disorder experiencing an acute episode of mania or mania with mixed features. The primary objective of the study is to evaluate the efficacy of KarXT compared to placebo in treating symptoms of mania during a 3-week inpatient period. The duration of the study including screening, the double-blind inpatient treatment period and safety-follow-up is no more than seven weeks.