Abstract PURPOSE: Medication nonadherence is common in the treatment of patients with severe mental illness and is a frequent cause of relapse. Different formulations have been developed in an effort to improve medication adherence. The aim of this study was to explore whether there are differential clinical outcomes between two different formulations of olanzapine (orodispersible tablets [ODTs] vs standard oral tablets [SOT]) for the treatment of nonadherent patients with schizophrenia or bipolar disorder. METHODS: Data for this analysis were from an observational study conducted in Europe (N=903). Adult schizophrenia and bipolar disorder patients in outpatient settings who initiated or changed to either olanzapine ODT or SOT according to physician decision within the last 45 days were eligible for enrollment. The follow-up period was 1 year. Of the 903 participants, 266 nonadherent patients (Medication Adherence Rating Scale score 0-4 at baseline) were included in the analysis. Clinical outcomes of interest were: 1) hospitalization and 2) relapse identified by the participating psychiatrist or hospitalization. An adjusted logistic regression model was fitted. RESULTS: Patients taking ODT had more severe illness at baseline (P<0.001) as assessed with the Clinical Global Impression with mean (standard deviation [SD]) scores of ODT 4.63 (1.03) and SOT 4 (1.16). In the regression models adjusted for potential confounders, patients taking ODT had significantly lower odds for hospitalization (odds ratio =0.355; 95% confidence interval =0.13-0.974) and relapse or hospitalization (odds ratio =0.368; 95% confidence interval =0.183-0.739), respectively. CONCLUSION: Nonadherent patients with schizophrenia or bipolar disorder treated with the orodispersible formulation were less likely to be hospitalized or suffer relapse compared to those patients taking the standard oral coated tablets.