Because variations in the HTR2A gene (encoding the 5-hydroxytryptamine type 2A receptor) and HTR2C gene (encoding the 5-hydroxytryptamine type 2C receptor) influence the binding affinities of antipsychotic medication, in previous studies, two genetic polymorphisms related to hyperprolactinemia in schizophrenic patients treated with classical and/or atypical antipsychotic treatment have been analyzed. This evidence concerns the gene HTR2A and hyperprolactinemia.