<prompt> One of the following drug causes least gain in weightQuetiapineZiprasidoneOlanzapineRisperidone  <response>: B Ziprasidone Risperidone, a benzisoxazole derivative, is more potent at 5HT2 than D2 receptor sites, like clozapine, but it also exerts significant a2 antagonism, a property that may contribute to its perceived ability to improve mood and increase motor activity. Risperidone is not as effective as clozapine in treatment resistant cases but does not carry a risk of blood dyscrasias. Olanzapine is similar neurochemically to clozapine but has a significant risk of inducing weight gain. Quetiapine is distinct in having a weak D2 effect but potent a1 and histamine blockade. Ziprasidone causes minimal weight gain and is unlikely to increase prolactin, but may increase QT prolongation. Aripiprazole also has little risk of weight gain or prolactin increase but may increase anxiety, nausea, and insomnia as a result of its partial agonist properties.ANTIPSYCHOTIC AGENTSNameUsualPOSide Effects Daily Dose, mgSedationCommentsClozapineClozaril2 0 0 - 600Agranulocytosis 1; weight gain; seizures; drooling; hyperthermia Requires weekly WBCRisperidone Risperdal observed with doses 6 mg qd2-6OrthostasisRequires slow titration; EPSEsOlanzapineZyprexa10-20Weight gain Mild prolactin elevationQuetiapineSeroquel3 5 0 - 700Sedation; weight gain; anxiety Bid dosingZiprasidoneGeodon40-60Orthostatic hypotension Minimal weight gain; increases QT intervalAripiprazole Ability10-30Nausea, anxiety, insomnia0Mixed agonist antagonist 