DRD2 and Parkinson disease: Radioactive clozapine demonstrates rapid and transient occupancy of dopamine D2 receptors, dissociating in under 60 seconds (in comparison, haloperidol and chlorpromazine have receptor occupancy of 30 minutes), which contributes to the clinical effectiveness of atypical antipsychotics [16]; however, at chronic toxic doses, this rapid dissociation may diminish, leading to movement disorders similar to Parkinson's disease.