Antipsychotic medications, previously referred to as major tranquilizers or neuroleptics, are effective for the treatment of a variety of psychotic symptoms. Antipsychotics can be classified in several ways. One classification system is based on chemical structure; for example, phenothiazines and butyrophenones make up two chemical classes. We use the term conventional to signify older or first-generation antipsychotic drugs—to differentiate them from newer atypical or second-generation antipsychotics. Among the conventional antipsychotics, we distinguish between high- and low-potency agents because the level of potency predicts side effects. Although the term atypical antipsychotic lacks a single consistent definition, it generally refers to the newer antipsychotic medications that affect both 5-HT₂ and D₂ receptors. Atypical antipsychotics available in the United States include clozapine, olanzapine, risperidone, quetiapine, ziprasidone, and aripiprazole.