Clozapine antipsychotic drug molecule. Clozapine, marketed as Clozaril, is an atypical antipsychotic used to treat schizophrenia. It works by blocking receptors in the brain for the neurotransmitters dopamine and serotonin, the overactivity of which is associated with schizophrenia. It is only used as a last resort in patients that have not responded to treatment with at least two other antipsychotics due to the risk of potentially fatal side effects including agranulocytosis (lowered white blood cell count). Atoms are represented as spheres and are colour-coded: carbon (mid blue), hydrogen (green), nitrogen (dark blue) and chlorine (orange).