Fentanyl potency relative to morphine?

• A. 10x
• B. 50x
• C. 100x
• D. 1000x

Answer: (C)

Potency is about how much drug is needed to achieve the same effect. Fentanyl is extremely potent because it binds mu-opioid receptors with high affinity and it’s highly lipophilic, so it reaches the brain rapidly. This means very small doses produce the same analgesic effect as much larger doses of morphine. In practice, about 100 micrograms of fentanyl intravenously yields analgesia similar to 10 milligrams of morphine, illustrating a roughly 100-fold difference in potency. The other options fall outside the commonly cited range for equianalgesic dosing—10x would understate it, 50x is less typical, and 1000x would be unrealistically high.