This study is testing valbenazine, a medicine, to help people with schizophrenia, which is a mental health disorder affecting how a person thinks, feels, and behaves. The study compares valbenazine with a placebo, which looks like the medicine but has no active ingredients. This is a double-blind study, meaning neither the participants nor the researchers know who is getting the real medicine or the placebo until the study ends. About 400 participants will take part for 16 weeks, receiving valbenazine in addition to their usual antipsychotic medicine.

• The study lasts for about 16 weeks.
• Participants must be 18 or older with a stable schizophrenia diagnosis.
• Participants will not know if they are receiving the real medication or a placebo.

Participants must not be pregnant, breastfeeding, or have certain other health issues. People with a history of severe depression or those at risk of suicide may not join. This study will help understand if valbenazine can better manage schizophrenia symptoms when other treatments are not enough.