Inclusion Criteria:  Subject's parent(s)/legal guardian(s) is considered reliable by the Investigator and has agreed to provide support to the subject to ensure compliance with study treatment, visits, and protocol procedures. Male and female subjects between 10 and 12 years of age, inclusive. Subject weighs ≥70 pounds. Subjects who are receiving antipsychotic treatment for their medical condition, with a diagnosis of bipolar I disorder. Subjects must be considered stable, per investigator judgement. Subject is willing to abide by the contraception requirements for the duration of the study.  Exclusion Criteria:  Subject has a comorbid neuropsychiatric disorder that could interfere with participation in the study. Subject poses a current suicide risk as assessed by the Investigator or as confirmed by the baseline Columbia-Suicide Severity Rating Scale by a response of "Yes" to question numbers 4 or 5 with ideation or suicidal behavior occurring in the past 12 months (assessed at Screening and at Visit 2, Day 1). Subject has a diagnosis of diabetes or presents with pre-diabetes lab results (hemoglobin A1c ≥6%). Subject has a history of use of clozapine or use of long-acting injectable antipsychotic medication within 3 months prior to Screening. Subject has a DSM-5 (Diagnostic and Statistical Manual of Mental Disorders-5) diagnosis of moderate to severe alcohol disorder, or moderate to severe substance use disorder, within the 3 months prior to Screening. Subject has taken opioid agonists within the 14 days prior to Screening, or has taken long-acting opioid agonist within the 30 days prior to Screening, or has anticipated a need to take opioid medication during the study period (eg, planned surgery, including oral surgery), or has taken opioid antagonists including naltrexone (any formulation) and naloxone within 60 days prior to Screening. Subject is unable to swallow oral medications, as assessed by the Investigator. Subject has a positive urine drug screen for opioids (assessed at Screening and at Visit 2, Day 1). Subject has a positive cotinine test (assessed at Screening and at Visit 2, Day 1). Subject has an intellectual disability, as assessed by the Investigator. Subject has a history of intolerance or hypersensitivity to olanzapine or opioid antagonists, or any component of the study drug.