Olanzapine (Zyprexa^®) -- a drug that is licensed to treat schizophrenia and bipolar disorder -- works by blocking or lessening the effects of several chemicals in the brain. Olanzapine comes in tablet form and is usually taken once a day. As with any drug, there are possible side effects with olanzapine. Some of the more common side effects seen with this drug include dizziness, drowsiness, and constipation. A few of the conditions that you should let your healthcare provider know about before you take olanzapine include an enlarged prostate (benign prostatic hyperplasia or BPH), Alzheimer's disease or other forms of dementia, and low blood pressure (orthostatic hypotension).