Ondansetron treats postoperative nausea by blocking which receptor?

• A. Dopamine D2 receptor
• B. Serotonin 5-HT3 receptor
• C. Histamine H1 receptor
• D. Muscarinic acetylcholine receptor

Answer: (B)

Blocking serotonin 5-HT3 receptors is how ondansetron prevents postoperative nausea. During surgery, serotonin released in the gut activates 5-HT3 receptors on vagal afferents and in the chemoreceptor trigger zone, signaling the brain to induce vomiting. By antagonizing these receptors, ondansetron interrupts that signaling and reduces nausea and emesis. Other receptor targets like dopamine D2, histamine H1, or muscarinic receptors are involved in different antiemetic pathways, which is why those receptors are not the primary action of this drug.