Table 2.

Opioid Affinity to Mu Opioid Receptor*. Note: Lower Κ_i indicates higher binding affinity

Full agonist of MOR	Partial agonist of MOR	Κi (nM)
	Buprenorphine	0.22
Hydromorphone		0.37
Morphine		1.17
Fentanyl		1.35
Methadone		3.38
Oxycodone		25.87
Hydrocodone		41.58
Meperidine		450.10
Codeine		734.20

*Abbreviations: MOR, mu opioid receptor; Ki, equilibrium dissociation constant for the test compound; nM, nanomolar concentration

Adapted from Volpe et al. (2011)²⁰ and Wang et al. (2007)²¹