This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intravenous Anesthetic Agents, Subject name: Anaesthesia
The opioid contraindicated in patients on MAO inhibitor is 
Select and explain. 
A. codeine, B. Morphine, C. Fentanyl, D. Buprenorphine
C: Fentanyl
Answer: C: Fentanyl 
Explanation: Some opioid analgesics are associated with a risk of serotonin syndrome in combinations with MAOIs due to their serotonergic propeies. 1. Dextromethorphan, 2. methadone, 3. pethidine, 4. tramadol or 5. fentanyl should be avoided in patients on MAO inhibitor.