TABLE 1

Opioid receptors and ligands

Receptor and Site of Action	Effects	Agonist	Antagonist
μ
Systemic	Analgesia	DAMGO	CTOP
	Euphoria	Morphine	Naloxone
	Constipation	Fentanyl
	Respiratory depression	Endomorphins
		β-Endorphin
Peripheral	Analgesia	DiPOA	Alvimopan
	Constipation	HS731/AS006	Naloxone methiodide
	Reduced inflammation	Loperamide	Methylnaltrexone
		Frakefamide
		DALDA
δ
Systemic	Analgesia	DPDPE	Naltrindole
	Constipation	SNC 80	ICI 174,864
	Respiratory depression	Enkephalins	Naloxone
		Deltorphin
		β-Endorphin
Peripheral	Analgesia	UK-321,130	Naloxone methiodide
	Constipation
κ
Systemic	Analgesia	U-69593, U50,488	Norbinaltorphimine
	Diuresis	Bremazocine	Naloxone
	Dysphoria	Dynorphin A-B
Peripheral	Analgesia	Asimadoline	Naloxone methiodide
	Reduced inflammation	FE200665/CR845

DAMGO, [d-Ala²,N-Me-Phe⁴,Gly⁵-ol]-enkephalin; CTOP, d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH₂; HS731, 14-O-methyloxymorphone; DALDA, Tyr-Arg-Phe-Lys-NH₂; DPDPE, [d-Pen²,d-Pen⁵]-enkephalin; SNC 80, 4-(α-(4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl)-N,N-diethylbenzamide; ICI 174,864, N,N-diallyl-Tyr-Aib-Aib-Phe-Leu; U-69593, N-methyl-2-phenyl-N-[(5R,7S,8S)-7-(pyrrolidin-1-yl)-1-oxaspiro[4.5]dec-8-yl]acetamide; U50,488, trans-3,4-dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide.