Table 2.

MOR and KOR Agonists and Their Selectivities^129,148,149

Drug / Compound name:	Selectivity (estimated Ki [nM]) at the human receptor*			Approved for use?
	MOR	KOR	DOR
β-Endorphin	1.18	31.7	1 to 5.4	endogenous
Dynorphin A	32	0.5	1,000	endogenous
Enkephalin	1.77	506.17	200 to 1,430	endogenous
Morphine	2.16	50 to >2,000	1,545 to 2,500	USA (FDA) for analgesia
Oxycodone	780	>2,000	>10,000	USA (FDA) for analgesia
Fentanyl	1	169.9	152 to >1,000	USA (FDA) for analgesia
Pentazocine	5.4	2.6	114.5	USA (FDA) for analgesia
Butorphanol	0.12	0.22	12	USA (FDA) for analgesia
Buprenorphine	0.85 (partial agonism)	0.71 (antagonism)	3.7 (antagonism)	USA (FDA) for OUD
Nalfurafine* (TRK-820)	3.2 to 5.2	0.025 to 0.075	161 to 289	Japan (MHLW) for pruritus
EOM Salvinorin B	>1	0.32	>1	no
ICI 199,441	54	0.04	24	no
U50,488	>1,000	0.16	645	no
U69,593	>1,000	1.53	>1,000	no
RB-64	>10,000	0.59	>10,000	no
Salvinorin A	>10,000	1.82	>1,000	no
Triazole 1.1	>10,000	0.25	>2,000	no

^*Estimated nalfurafine Ki (nM) values are presented at the rat MOR, human KOR, and mouse DOR, respectively.