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3.6 Blood disorders

Leucocytosis1, leucopenia and eosinophilia can occur rarely with antipsychotic medicines; such blood disorders usually appear in the first 8–12 weeks of treatment. Other blood disorders reported with the use of antipsychotics include haemolytic anaemia, aplastic anaemia, neutropenia2, thrombocytopenia, and agranulocytosis3.

Clozapine is associated with a significant risk of agranulocytosis. Patients taking clozapine must be registered with a patient monitoring service which entails centralised monitoring of leucocyte and neutrophil count.

Among the older antipsychotics, phenothiazines have been most commonly implicated with agranulocytosis and neutropenia.

Factors which increase risk

Blood disorders or a history of blood disorders may increase the risk of antipsychotic-induced bone-marrow toxicity. Concomitant use of myelosuppressive drugs might also increase the risk of blood disorders.

Risk-reduction measures

Antipsychotics should be avoided or used with caution in patients with blood disorders.

Symptoms such as sore throat or unexplained infection should be watched for and should prompt blood tests including white cell count.

Specific risk-reduction measures have been devised for clozapine. For warning against the concomitant use of clozapine and prolonged-acting antipsychotic injections, see under Clozapine.


The antipsychotic should be stopped if it is suspected to be causing clinically important blood disorder.

This learning module discusses noteworthy risks for antipsychotics. Summaries of product characteristics and the BNF should be consulted for a fuller account of the adverse effects and warnings for individual antipsychotics.

  1. An increase in the number of white cells in the blood, usually in response to inflammation. Leucocytosis can also be abnormally triggered by drugs
  2. Marked deficiency of a type of white blood cell (neutrophil) responsible for ingesting bacteria
  3. Marked deficiency of a type of white blood cells (granulocytes) essential for immune functioning