There is a deficiency of hematopoietic stem cells in the bone marrow due to direct toxicity by external agents, immune destruction of stem cells, or bone marrow replacement by malignancy or fibrosis. Rarely, pancytopenia is congenital.

Acquired pancytopenia is due to drugs (sulfonamides, anticonvulsants), viral infections, and autoimmune disease. It is an expected side effect of chemotherapeutic treatment.

It is an extremely rare idiosyncratic reaction to psychotropic agents [1]. There are case reports with carbamazepine , valproate , olanzapine , and clozapine .

When it does occur, it can be severe and life threatening. It can be seen within a few days of starting the medication . Stopping the medication rapidly brings the blood counts back to normal.