Aripiprazole's mechanism of action is different from those of the other FDA-approved atypical antipsychotics (., clozapine , olanzapine , quetiapine , ziprasidone , and risperidone ).         Rather than acting as a pure antagonist of the dopamine D 2 receptor , aripiprazole shows functional selectivity at the D 2 receptor, acting as a silent antagonist of some subpopulations of D 2 receptors but as a high-efficacy partial agonist ( intrinsic activity = 75%) of other D 2 -receptor subpopulations.  It appears to show predominantly antagonist activity on postsynaptic D 2 receptors and partial agonist activity on presynaptic D 2 receptors.  Aripiprazole is also a partial agonist of the D 3 receptor .  In healthy human volunteers, D 2 and D 3 receptor occupancy levels are high, with average levels ranging between approximately 71% at 2 mg/day to approximately 96% at 40 mg/day.   Most atypical antipsychotics bind preferentially to extrastriatal receptors, but aripiprazole appears to be less preferential in this regard, as binding rates are high throughout the brain. 
An assessment for an underlying cause of behavior is needed before prescribing antipsychotic medication for symptoms of dementia .  Antipsychotics in old age dementia showed a modest benefit compared to placebo in managing aggression or psychosis, but this is combined with a fairly large increase in serious adverse events. Thus, antipsychotics should not be used routinely to treat dementia with aggression or psychosis, but may be an option in a few cases where there is severe distress or risk of physical harm to others.  Psychosocial interventions may reduce the need for antipsychotics.