Objective:: To illustrate the complexities of clozapine metabolism with the use of therapeutic drug monitoring.
Methods:: We describe a case of clozapine toxicity in a patient with schizophrenia treated with the combination of clozapine, valproate and haloperidol.
Results:: A 24-year-old CYP2D6 poor metaboliser developed clozapine toxicity corresponding to the additive effects of haloperidol, and increasing clozapine and valproate doses.