This study tests a new medicine, SEP-363856, for treating schizophrenia, a mental illness causing hallucinations and delusions (seeing or hearing things that aren’t there and having strong false beliefs). The trial will compare this medicine to a placebo, which is a fake treatment with no medicine in it. It's called "double-blind," meaning neither the doctors nor the patients know who gets the real medicine or the placebo.

Participants must be 18 to 65 years old and have had a recent flare-up of symptoms, requiring hospital care. They should also have a high score on the PANSS test, which measures the severity of schizophrenia symptoms. People with other serious mental health disorders or substance use issues are not eligible.

• The study will take place across multiple locations.
• Participants will receive either the study medicine or a placebo.
• Participants may need to visit the study site multiple times.

Participants should use two types of birth control or remain abstinent. This study checks if SEP-363856 can help people with severe schizophrenia symptoms. There are risks, such as side effects from the medication, and not all participants will receive the active drug.