What serious side effect must be monitored in patients on clozapine?

Clozapine is an atypical antipsychotic that is particularly effective in treatment-resistant schizophrenia. One of the most serious side effects associated with clozapine is neutropenia, which is a potentially life-threatening condition characterized by a dangerously low level of neutrophils, a type of white blood cell crucial for fighting off infections. Neutropenia can increase the risk of serious infections and is a significant reason why patients on clozapine require regular monitoring of their blood counts.

The monitoring process is necessary due to the risk of agranulocytosis, which occurs in a small percentage of patients but can lead to severe complications if not detected early. The risk requires that healthcare providers use a structured monitoring protocol, frequently checking the patient's complete blood count, particularly during the initial months of treatment.

The other options, while related to general health considerations, do not carry the same level of severity or specific monitoring requirements associated with clozapine treatment as neutropenia does. Hyperglycemia, hypotension, and severe headache can occur with clozapine, but these side effects are less critical and do not necessitate as rigorous or frequent monitoring as the risk of neutropenia does.