The primary objective for this study is to evaluate the efficacy of NBI-1117568 compared with placebo on improving manic symptoms in adults with bipolar I disorder who are currently experiencing an episode of mania with or without mixed features.

Key Inclusion Criteria:

• Participant has a primary diagnosis of bipolar I disorder.
• The participant has had at least 1 prior documented manic episode that required treatment.
• The participant is experiencing an acute manic episode or manic episode with mixed features, with or without psychotic symptoms.

Key Exclusion Criteria:

• Any unstable or poorly controlled medical condition or chronic disease (including history of neurological, hepatic, renal, cardiovascular, gastrointestinal, pulmonary, autoimmune, or endocrine disease that may affect study participation or results), or malignancy within 90 days before the start of screening.
• Primary diagnosis is not bipolar I disorder.
• History of clozapine treatment for treatment-resistant psychosis.
• History of psychiatric hospitalization(s) for ≥30 consecutive days during the 90 days before the start of screening.

Note: Additional inclusion/exclusion criteria may apply, per protocol.