The invention relates to methods and compositions for treating schizophrenia or bipolar disorder (in particular, mania) by using a combination of a synaptic vesicle protein 2A (SV2A) inhibitor and an antipsychotic or their pharmaceutically acceptable salts, hydrates, solvates, polymorphs, and prodrugs thereof. The methods and the compositions can be used for treating one or more positive and/or negative symptoms, as well as cognitive impairment, associated with schizophrenia or bipolar disorder (in particular, mania).
