The combination of olanzapine and samidorphan is used to treat the symptoms of schizophrenia (a mental illness that causes disturbed or unusual thinking, loss of interest in life, and strong or inappropriate emotions) in adults. It is also used alone or with other medications to treat episodes of mania (frenzied, abnormally excited or irritated mood) in adults with bipolar disorder (manic depressive disorder; a disease that causes episodes of depression, episodes of mania, and other abnormal moods). The combination of olanzapine and samidorphan is also used to prevent episodes of mania in adults with bipolar disorder. Olanzapine is in a class of medications called atypical antipsychotics. It works by changing the activity of certain natural substances in the brain. Samidorphan is an opioid antagonist. It works to reduce possible side effects from olanzapine, including weight gain.