Name	Info	Provider	Link
	subscription/membership/fee required	HighWire	http://molpharm.aspetjournals.org/cgi/pmidlookup?view=long&pmid=32665252
Opioid receptors - overview and references	free resource	Guide to Pharmacology	https://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=50