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Objective: To assess the effectiveness of olanzapine for treating schizophrenia and to assess if olanzapine promotes a better quality of life than first-generation antipsychotics (FGAs).

Method: Multicenter, naturalistic, randomized controlled study, comparing olanzapine with FGAs, at hospitalization and during a 9-month follow-up. Outcome assessors were blind to the allocated drug. The dose of antipsychotic was determined by doctors according to their clinical practice routines. Data collection was performed from April 1999 to August 2001.

Results: 197 patients with DSM-IV-diagnosed schizophrenia were allocated to olanzapine (N = 104) and FGA (N = 93). Patients taking olanzapine showed greater improvements in Positive and Negative Syndrome Scale (PANSS) negative symptoms (mean difference = 2.3, 95% CI = 0.6 to 4.1) and general psychopathology (mean difference = 4.0, 95% CI = 0.8 to 7.2) subscales and fewer incidences of tardive dyskinesia (RR = 2.4, 95% CI = 1.4 to 4.2, p < .0001). Olanzapine was also associated with greater improvement in a number of health-related quality-of-life outcomes on the Medical Outcomes Study 36-item Short-Form Health Survey, including physical functioning (mean difference = 6.6, 95% CI = 1.2 to 11.9), physical role limitations (mean difference = 13.7, 95% CI = 3.0 to 24.3), and emotional role limitations (mean difference = 12.1, 95% CI = 0.7 to 23.5). Patients taking olanzapine gained significantly more weight during the trial than patients taking FGAs, with a correspondent endpoint increase in the body mass index (BMI) of 28.7 versus 25.3 (p < .001).

Conclusion: Compared with FGAs, olanzapine has advantages in terms of improvements of negative symptoms and quality of life. It is also associated with fewer incidences of tardive dyskinesia and greater increases in weight and BMI. These findings are highlighted by the naturalistic approach adopted in this trial.