Conducted 4 clinical trials in the US, Europe, Africa, Australia, and the Middle East to assess the efficacy and safety of olanzapine (OLZ) in comparison with placebo and haloperidol. Ss were more than 2,500 patients with schizophreniThese trials indicated that OLZ is more effective than placebo and at least as effective as haloperidol in treating the positive symptoms of schizophrenia, as assessed by total score and the positive symptom subscale of the Brief Psychiatric Rating Scale, and has superior activity, when compared to haloperidol, toward negative symptoms of disease. OLZ also had benefits over haloperidol in terms of associated secondary mood symptoms, global functioning and quality-of-life measures. Extrapyramidal syndromes were minimal in Ss on OLZ, and the rates of treatment-emergent tardive dyskinesia in OLZ recipients were significantly lower than among haloperidol recipients. There was no evidence that OLZ caused hematoxicity, and the drug was associated with fewer instances and lower severity of hyperprolactinemia than haloperidol. Adverse events most often reported were dry mouth, weight gain, increased appetite, and subjective sedation.