DRD2 and schizophrenia: Effects of antipsychotic drugs with antagonistic property mediated by blockade of postsynaptic dopamine D2 receptors can be evaluated by positron emission tomography (PET) studies for determining the occupancy of dopamine D2 receptors in schizophrenia patients treated with first-generation antipsychotics, e.g., haloperidol [1], [2] and second-generation antipsychotics, e.g., risperidone [3], antagonists of dopamine D2 receptors.