endorphin vs enkephalin

endorphin and enkephalin both are nouns.

Word	Noun	Adjective	Verb	Adverb
endorphin	Yes	No	No	No
enkephalin	Yes	No	No	No

As nouns, enkephalin is a hyponym of endorphin; that is, enkephalin is a word with a more specific, narrower meaning than endorphin:

endorphin: a neurochemical occurring naturally in the brain and having analgesic properties
enkephalin: an endorphin having opiate qualities that occurs in the brain and spinal cord and elsewhere

Other hyponyms of endorphin include beta endorphin.

endorphin (noun)	enkephalin (noun)
a neurochemical occurring naturally in the brain and having analgesic properties	an endorphin having opiate qualities that occurs in the brain and spinal cord and elsewhere