The case for multiple opiate receptors

As recently as ten years ago the opiate receptor was demonstrated biochemically for the first time and it was assumed that opiate drugs produced their psychotropic actions through a unique opiate receptor. Today compelling evidence from behavioral, pharmacological and biochemical studies indicates the existence of at least four receptor classes, μ, δ, κ and σ. The constellation of neuropharmacological actions of opiates as well as those of the three major classes of opioid peptides (β-endorphin, the enkephalins and dynorphin-related peptides) are now thought to occur by an interaction with a combination of these sites.