enkephalin

This term is used exclusively within specialized biochemical and medical contexts. It refers to a specific class of neuropeptides that function as natural painkillers within the body, acting on delta and mu opioid receptors to dampen the perception of pain.

As a chemical substance and a specific biological molecule, it is treated as an uncountable noun. It is typically used in the singular to describe the substance in general or the specific peptide chain, rather than as a countable object.