Which opioid is noted for having a more potent effect at mu-opioid receptors compared to morphine?

Fentanyl is noted for its potency at mu-opioid receptors and is significantly stronger than morphine. This increased potency arises from its affinity for the mu-opioid receptor, leading to a more profound effect at lower doses compared to morphine. Fentanyl's lipid solubility allows it to rapidly penetrate the central nervous system, contributing to its effectiveness in pain management and the quicker onset of action.

While hydromorphone, buprenorphine, and oxycodone also interact with mu-opioid receptors, they do not exhibit the same level of potency as fentanyl when comparing equivalent doses. Hydromorphone is indeed stronger than morphine but not to the same degree as fentanyl, which is approximately 50 to 100 times more potent. Buprenorphine is a partial agonist at mu-opioid receptors, which limits its maximum effect compared to full agonists like fentanyl and morphine. Oxycodone, while also effective, does not surpass the potency of fentanyl either.

Thus, fentanyl stands out in terms of its potency at mu-opioid receptors compared to morphine, making it the correct choice.