CSF2 and neutropenia: Although the mechanism by which lithium increases the number of neutrophils is not fully clear,9 it is hypothesised to be related to the increased production of granulocytes via the enhanced action of colony-stimulating factor on colony-forming cells.10–13 Moreover, lithium causes both acute and chronic increases in leucocytes and neutrophils10 and has been used to increase neutrophil counts in patients who have developed neutropenia while on clozapine.11–13 In addition, the dosage of lithium carbonate can affect the leucocyte-increasing effect.