Granisetron primarily functions as a serotonin 5-HT3 receptor antagonist, exerting its antiemetic effects by blocking the action of serotonin at these receptors. By antagonizing the 5-HT3 receptors, granisetron inhibits serotonin-mediated signaling that contributes to nausea and vomiting. Unlike some other antiemetic drugs, granisetron does not directly affect dopamine receptors (as seen with dopamine receptor antagonists like metoclopramide) or muscarinic receptors (as seen with anticholinergic drugs like scopolamine). Its specificity for serotonin receptors makes it a valuable option for managing chemotherapy-
