The primary objective of this study is to evaluate the efficacy of NBI-1065890 compared with placebo for the treatment of tardive dyskinesia (TD) in adult participants.

Key Inclusion Criteria:

• Medically confirmed diagnosis of schizophrenia, schizoaffective disorder, bipolar disorder, or major depressive disorder (MDD) as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) for at least 3 months prior to screening.
• Medically confirmed diagnosis of neuroleptic-induced TD as defined in the DSM-5 for at least 3 months prior to screening.
• Moderate or severe TD (AIMS Item 8, severity of abnormal movement overall) as assessed by a blinded, external AIMS video reviewer using a video recording of the participant's AIMS assessment administered at the clinical site by a blinded, certified site AIMS rater. The AIMS dyskinesia total score (sum of Items 1 to 7) must be ≥6 as assessed by the blinded, external AIMS video reviewer.

Key Exclusion Criteria:

• Comorbid parkinsonism (drug-induced or otherwise) or more than a minimal level of extrapyramidal signs/symptoms, as documented by a score on the Modified Simpson-Angus Scale (mSAS) (excluding Items 8 and 10) >6 at screening or Day -1 (baseline) or a score >3 in any one item (excluding Items 8 and 10).
• Barnes Akathisia Rating Scale (BARS) global clinical assessment score ≥2 at screening or Day -1.
• Brief Psychiatric Rating Scale (BPRS) total score ≥50 at screening or Day -1.
• Hospitalized for schizophrenia, schizoaffective disorder, bipolar disorder, or MDD within 6 months of screening.
• Participant has an unstable medical condition or unstable chronic disease.
• Any known history of neuroleptic malignant syndrome (NMS).

Note: Other protocol-defined inclusion and exclusion criteria may apply.