The atypical antipsychotic agent clozapine is associated with a lower propensity for extrapyramidal symptoms than classical antipsychotic agents. The pharmacokinetics of clozapine are affected by wide interpatient variability and a potential for drug interactions. Some studies have shown a relationship between plasma concentrations, duration of treatment and antipsychotic clinical response. Clozapine (mean 274.2 mg/day; n = 490) had a greater preventive effect on suicidality among patients with schizophrenia or schizoaffective disorder at high risk for suicide than olanzapine (mean 16.6 mg/day; n = 490) in a randomised, rater-blinded, multicentre study (p < 0.05; a 22-24% improvement). Other prospective noncomparative trials of the effects of clozapine on suicidal ideation or attempts endorsed these results, while results from retrospective trials are equivocal. Clozapine is commonly associated with sedation, hypersalivation, tachycardia, dizziness, constipation and orthostatic hypotension. Agranulocytosis, diabetes mellitus and weight gain may also occur.