To compare the relative effectiveness and tolerability profile, in terms of Number Needed to Treat (NNT) for all causes of medication discontinuation and Number Needed to Harm (NNH) for 7% of increased of body weight of olanzapine, risperidone, typical (oral and depot) and other atypical antipsychotic medications (quetiapine and amisulpride) in previously untreated outpatients with schizophrenia during 36-month follow-up.

NNTs (NNHs) mean the number of patients needed to be treated with one antipsychotic instead of another to prevent (produce) one negative outcome.

Previously untreated patients with schizophrenia were defined as patients who i) had never received antipsychotic treatment for schizophrenia and ii) had not received antipsychotic treatment in the 6 months prior to study inclusion. Rate of medication discontinuation for any cause during the 36 months post initiation was calculated for olanzapine (28.9%), risperidone (36.2%), typicals (44.5%) and other aypicals) (34.7%). Cox and logistic regression models were employed to adjust for treatment group differences at baseline and NNTs and NNHs with their 95% confidence intervals were calculated.

The NNTs for all-cause discontinuation of olanzapine were: 12.2.(95% CI: 5.8; 229.7) for olanzapine vs. risperidone, and 6.2 (3.1 ; 37.8) for olanzapine vs. typicals. The NNH for 7% weight gain was -3.7 (-2.6 ; -9.5) for olanzapine vs. typicals.

Treatment effectiveness and tolerability varied among medications. The NNTs for olanzapine therapy were consistently better when compared to other treatment cohorts. The weight-gain NNHs for olanzapine treatment were less favourable when compared to other antipsychotic medications.