Antipsychotic drugs (APDs) are therapeutic in psychotic disorders. They are not specific treatments for schizophrenia (SZ) but useful in bipolar disorder (BD), psychotic depression, Alzheimers disease, and other psychotic diagnoses. In this perspective, we discuss the actions of APDs for the treatment of both SZ and bipolar-1 disorder (BD-1) with a specific focus on the implications of these data for the whole group of psychotic diagnoses. Both schizophrenic and BD-1 are characterized by several symptom dimensions, some overlapping and some distinctive. We discuss a dimensional approach to the diagnosis of BD and SZ and suggest that psychosis is an important dimension of each. In order to define the dimension of psychosis more carefully would require additional research to fill in the gaps in our knowledge. We propose that psychosis is a dimension that cuts through many psychiatric disorders, and the use of this dimension may be useful for clinical and research progress. We discuss the kinds of data necessary to further support the dimensional aspects of psychosis.