Olanzapine is an atypical antipsychotic medication, previously expected to be safe in terms of hematological side effects and an alternative choice to clozapine in patients who develop hematotoxicities. However, since olanzapine was introduced to the market, a lot of cases reports have been published revealing it could cause hematoxicity. Some of them indicate that olanzapine induces agranulocytosis. Because of that, it raises the concerns about hematological safety of olanzapine.

To date, no review discusses this topic specifically, so we conducted a systemic review to explore and address this issue.

We searched Pubmed, Google Scholar, Ovid and Medline databases for articles between 1998 and 2015 that include keywords olanzapine, leukopenia, neutropenia, and agranulocytosis.

A total of 38 publications were identified. The case reports included patients aged 16 to 83 years. Doses ranged from 2.5 to 30 mg. After starting treatment, onset of hematotoxicity varied from the first day to 2–3 years, but most commonly within the first month. Also, olanzapine could induce leukopenia in patients who have never developed drug-related leukopenia.

Among antipsychotic medications, olanzapine is the third leading cause of neutropenia and the second leading cause of atypical antipsychotic medication. Because of the small body of literature regarding the hematotoxic side effects of olanzapine, we encourage further research to understand the mechanism by which olanzapine causes granulocytopenia. The identification of risk factors could facilitate the development of new surveillance guidelines in patients taking olanzapine. We recommend that the guidelines of using and monitoring olanzapine need to be reconsidered.

The authors have not supplied their declaration of competing interest.