This study is testing a drug called *KarXT* to see how well it works and if it's safe for treating **manic episodes** in people with **Bipolar-I disorder**. A manic episode is a period when someone feels extremely excited, energetic, or irritable. The study is *randomized* (participants are randomly assigned to different groups), *double-blind* (neither participants nor researchers know who is getting the study drug or a placebo), and *placebo-controlled* (some participants receive a placebo, which is a harmless pill that looks like the study drug). Participants must have a diagnosis of Bipolar-I disorder and be experiencing a manic episode that needs hospitalization. Before starting, participants must stop taking other mental health medications. The study lasts up to 7 weeks, including a 3-week stay in a hospital setting. **Key Points:** - The study requires a 3-week hospital stay. - Participants need to stop taking other mental health medications 14 days before starting. - The study lasts no more than 7 weeks in total. If you or someone you know wants to join, make sure they understand the need for hospitalization and medication changes.