A type of drug used to treat symptoms of psychosis. These include hallucinations (sights, sounds, smells, tastes, or touches that a person believes to be real but are not real), delusions (false beliefs), and dementia (loss of the ability to think, remember, learn, make decisions, and solve problems). Most antipsychotic agents block the action of certain chemicals in the nervous system. Also called antipsychotic and neuroleptic agent.