The primary objective for this study is to evaluate the effect of adjunctive valbenazine versus placebo on symptoms of schizophrenia in participants who have inadequate response to antipsychotic treatment.

Phase 3, randomized, double-blind, placebo-controlled study to evaluate the efficacy, safety, and tolerability of valbenazine when administered orally once daily as adjunctive treatment in participants with schizophrenia who have had an inadequate response to antipsychotics. The study will enroll approximately 400 participants with a diagnosis of schizophrenia. The expected duration of study participation for each participant is approximately 16 weeks.

Inclusion Criteria:

• Participants must meet all of the following inclusion criteria:

1. Completed written informed consent.

2. At the time of signing the informed consent, participant must be ≥18 years of age

3. Medically confirmed diagnosis of schizophrenia as defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).

4. The initial diagnosis of schizophrenia must be ≥1 year before the screening visit.

5. Plasma levels for at least 1 of the participant's antipsychotic medications must be detectable by an available assay.

6. The participant is treated with a stable regimen antipsychotic medication.

7. Must meet all of the following criteria at the screening visit and Day 1:

   • PANSS total score ≥70

   • PANSS score of ≥4 on at least 1 of the following:

     • P1 (delusions)
     • P3 (hallucinations)
     • P6 (suspiciousness)
     • G9 (unusual thought content)

   • CGI-S score ≥4

   • Stable background antipsychotic medication dose between the screening visit and Day 1

   • Stable PANSS total score between the screening visit and Day 1

8. The participant is outpatient with stable symptomatology

9. The participant must have an adult informant (for example, a family member, relative, partner, social worker, caseworker, residential facility staff, or nurse).

10. Female participants of childbearing potential must agree to use contraception consistently from the screening visit until 30 days after the last dose of study drug or final study visit, whichever is longer.

11. Male participants must agree to use contraception consistently from screening until 30 days after last dose of study treatment.

Exclusion Criteria:

• Participants will be excluded from the study if they meet any of the following criteria:

  1. Pregnant or breastfeeding or plans to become pregnant during the study. This criterion must be reconfirmed prior to the first dose of study treatment on Day 1.
  2. Known hypersensitivity to any component of the formulation of valbenazine.
  3. Has history of treatment resistant schizophrenia.
  4. Evidence of depression as measured by a Calgary Depression Scale for Schizophrenia (CDSS) score ≥11 at the screening visit or Day 1.
  5. Participants with any suicidal behavior or suicidal ideation within 6 months before the screening visit or Day 1.
  6. Diagnosis of moderate or severe substance use disorder within the 6 months before the screening visit.
  7. Have a clinically significant unstable medical condition within 60 days before the screening visit in the judgement of the investigator or any laboratory value outside the normal range that is considered by the investigator to be clinically significant at the screening visit.
  8. Prior (within 6 months of the screening visit) or concomitant use of any VMAT2 inhibitor.