Study in Adolescents With Schizophrenia or Bipolar Disorder

Inclusion Criteria: * Participants must have a diagnosis of bipolar I disorder and display an acute manic or mixed episode (with or without psychotic features) or a diagnosis of schizophrenia according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition - Text Revision (DSM-IV-TR)and confirmed by the Kiddie Schedule for Affective Disorders and Schizophrenia for School Aged Children-Present and Lifetime (K-SADS-PL). * Participants with a diagnosis of schizophrenia must obtain a Brief Psychiatric Rating Scale for Children (BPRS-C) total score \>30, with a minimum score of 3 on at least one of the following items at both screening and randomization - hallucinations, delusions, peculiar fantasies. * Participants with a diagnosis of bipolar I disorder must have a Young Mania Rating Scale (YMRS) total score greater than or equal to 15 at both screening and randomization. * Has given assent (when applicable); and has a parent or authorized legal representative who has given informed consent, is reliable, has a level of understanding sufficient to permit participant to perform all tests and examinations required by the protocol, and understands the nature of the study. Exclusion Criteria: * History of mental retardation, current comorbid autism, or current comorbid Pervasive Developmental Disorder. * Have DSM-IV-TR substance (except nicotine and caffeine) dependence within the past 30 days prior to randomization. * Been judged clinically to be at any suicidal risk. * History of allergic reaction or hypersensitivity to olanzapine. * Receiving current pharmaceutical treatment for weight management or are participating in a structured behavioral diet and/or exercise weight loss program. * Other antipsychotics, mood stabilizers, or anticonvulsants (for mood stabilization) used for the primary study conditions (bipolar I disorder or schizophrenia) * Have acute, serious, or unstable medical conditions * Have any illness such that death is anticipated within 1 year or intensive care unit hospitalization for the illness is anticipated within 12 months (365 days). * Have had one or more seizures without a clear and resolved etiology. * Baseline alanine aminotransferase (ALT) values greater than or equal to 2 times the upper limit of normal (ULN) of the performing laboratory or aspartate aminotransferase (AST) values greater than or equal to 2 times the ULN or total bilirubin values greater than or equal to 1.5 times the ULN at screening. * Have leukopenia or history of leukopenia without a clear and resolved etiology or known history of agranulocytosis (absolute neutrophil count \<500 cubic millimeter \[mm\^3\], \<0.5 GI/L, or \<0.5 10E\^3/microliters \[μL\]) during the participant's lifetime. * Prolactin level of \>200 nanograms per milliliter (ng/mL) \[\>200 micrograms per liter (ug/L), or \>4228 milli-International unit per liter (mIU/L)\] at screening. * Have QTc (Bazett's) \>450 milliseconds (males) or \>460 milliseconds (females) at screening. * Previously been randomized in this study and/or participated in a clinical trial of another investigational drug, including olanzapine, within 1 month (30 days) prior to screening. * Currently prescribed olanzapine for greater than or equal to 5 days within 1 month (30 days) prior to screening. * Are investigator site personnel directly affiliated with this study and/or their immediate families OR are employed by or representatives of Lilly. * Pregnant or nursing. * Have received treatment within the last 30 days with an investigational new drug that has not received regulatory approval for any indication at the time of study entry. * Treatment with clozapine within 14 days prior to randomization. * Participants who have used olanzapine (that is, oral olanzapine, intramuscular \[IM\] olanzapine, or olanzapine orally disintegrating tablets) and have had treatment withdrawn due to clinically significant and/or intolerable adverse effects, or who have exhibited a lack of efficacy/response to treatment to olanzapine including treatment resistance.