Buprenorphine is what type of Mu receptor ligand?

• A. Full agonist
• B. Partial agonist
• C. Antagonist
• D. Inverse agonist

Answer: (B)

Buprenorphine binds to mu opioid receptors with high affinity but only partially activates them. This partial intrinsic activity means it provides some analgesia, but not the full effect seen with classical opioids like morphine or fentanyl. The high affinity and partial activation give a ceiling to certain effects, notably respiratory depression and euphoria, reducing overdose risk compared with full agonists. Its strong receptor binding also means it can block other opioids from binding, which is why it can precipitate withdrawal in someone already dependent on full agonists if given too soon. In contrast, a full agonist would produce maximal receptor activation, while an antagonist would block activation altogether, and an inverse agonist would reduce baseline receptor activity.