Olanzapine (Trade name: Zyprexa) is an antipsychotic in the atypical antipsychotic class commonly used in the treatment of schizophrenia and bipolar disorder.
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Smoking induces CYP1A2, which increases the metabolism of olanzapine. When the smoking stops or if a patient quits, this can lead to supratherapeutic levels of olanzapine! Conversely, if patients are discharged from an inpatient setting and start smoking again, this can lead to rapid decreases in plasma olanzapine levels, resulting in relapse of psychotic symptoms.[2] There is a very high prevalence of smokers in the schizophrenia population, making this a very clinically important issue to be aware of.