This document discusses the pathophysiology of emesis and summarizes various drug classes that can be used as antiemetics, including: 1. Serotonin 5-HT3 antagonists like ondansetron, granisetron, and dolasetron which are potent antiemetics even though their site of action is in the vomiting center and chemoreceptor trigger zone. 2. Dopamine D2 antagonists like metoclopramide and domperidone which act on the chemoreceptor trigger zone but metoclopramide has more side effects due to crossing the blood brain barrier. 3. Antihistamines, anticholiner