This study looks at weight gain in children and teens with schizophrenia or bipolar I disorder. It compares the changes in body mass index (BMI) Z-score, a measure of weight adjusted for height, after treatment with two medications: OLZ/SAM and olanzapine. Participants should be between 10-17 years old, diagnosed according to the DSM-5 (a manual used to diagnose mental disorders), and have support from family or a legal guardian. They should not be a danger to themselves or others and must not have certain health conditions, like major depression or a history of seizures. Participants cannot have used certain medications, like opioids or long-acting antipsychotics, before the study.

• The study involves taking medication and monitoring weight changes.
• Participants must have a guardian for outpatient care.
• Certain health conditions or recent medication use may exclude participation.