BackgroundOff-label use of a drug not according to its regulatory labeling has become common in medicine, especially in the field of psychiatry. Mood stabilizers are intended to be used to attenuate mood fluctuations in bipolar disorder, but their use has spread to patients with schizophrenia, as it provides greater control of impulsivity and aggressiveness. Sodium valproate is one of the most frequently used mood stabilizers in psychiatry. This study determined the prevalence of off-label use of sodium valproate for schizophrenia and schizoaffective disorder in Abarbanel Psychiatric Hospital and the demographic and clinical characteristics associated with its use.MethodsRetrospective study of patients hospitalized in 2011–2012 with a diagnosis of schizophrenia or schizoaffective disorder in one of three general psychiatric wards.ResultsValproate use was significantly lower in the geriatric group (11.6% vs. 20.1%, chi square  = 4.7, p = .03), in patients with schizophrenia (14.1% vs. schizoaffective disorder (35.2%), chi square  = 29, p<.001) and in patients receiving both atypical and typical antipsychotics (23.3% vs. 16.4%, p = .04). In multivariate logistic regression analysis, diagnosis and the combination of atypical and typical antipsychotics predicted the use of sodium valproate. The number of other medications prescribed did not predict sodium valproate use.ConclusionsOff-label use of sodium valproate in psychiatric patients with schizophrenia or schizoaffective disorder is extensive, especially in younger patients and those with schizoaffective disorder. More research is needed to determine whether it is being prescribed appropriately.