DRD2 and Alzheimer disease: Indeed, antipsychotics are among some of the least selective medications in terms of receptor antagonism, and it is still unknown how aging and/or AD pathogenesis influence D2R, 5-HT2A and other important target receptors, including histaminergic, adrenergic, muscarinic, sigma, and serotonergic and dopaminergic receptors in other brain areas (41).