In a preclinical study by Pitsikas and Borsini (1996), a 5HT3 receptor antagonist, itasetron, demonstrated procognitive effects, and in a clinical trial by Zhang and collaborators (2006), another 5HT3 antagonist, ondansetron, was added to an on-going treatment with haloperidol and improved negative symptoms, general psychopathology, and cognitive functions in patients with schizophrenia. This evidence concerns the gene HTR3A and schizophrenia.