A Study to Evaluate the Efficacy and Safety of KarXT for the Treatment of Manic Episodes in Bipolar-I Disorder

Inclusion Criteria * Participants must have a primary diagnosis of Bipolar-I disorder established by a comprehensive psychiatric evaluation. * Participants must be experiencing an acute episode or relapse of mania or mania with mixed features (≤ 3 weeks). * Participants must require hospitalization for the acute exacerbation or relapse of mania. * Participants must have all psychotropic medications washed out in no more than 14 days prior to the first dose of the study drug. * Participants must have a Young Mania Rating Scale (YMRS) score of ≥ 20 at Screening and at Baseline. * Participants must have a Clinical Global Impressions-Bipolar (CGI-BP) ≥ 4 at Screening and at Baseline. Exclusion Criteria: * Participants must not have any primary Diagnostic and Statistical Manual of Mental Disorders (5th Edition, Text Revision) (DSM-5-TR) disorder, other than BP-I with mania or mania with mixed features within 12 months before screening, including BP-I with depression (for previous 3 months only), BP-II disorder, borderline personality disorder, major depressive disorder, and primary psychotic disorder, with the exception of mild anxiety disorders. * Participants must not have a primary diagnosis of BP-I with rapid cycling (≥ 4 distinct mood episodes in one year). * Participants must not have a DSM-5-TR diagnosis of moderate to severe substance use disorder (except tobacco use disorder) within the 12 months before screening, or current use as determined by urine toxicology screen or alcohol test. * Participants must not be at risk for suicidal behavior at screening or the baseline visit as determined by the Investigator's clinical assessment and the Columbia-Suicide Severity Rating Scale (C-SSRS). * Participants must not have a history of irritable bowel syndrome (with or without constipation) or serious constipation requiring treatment within the last 6 months. * Participants must not have a history or high risk of urinary retention, gastric retention, or untreated narrow-angle glaucoma. * Other protocol-defined Inclusion/Exclusion criteria apply.