enkephalin

From Ancient Greek ἐγκέφαλος (enképhalos, “brain”) +‎ -in.

enkephalin (plural enkephalins)

1. (biochemistry) Any of a group of pentapeptide endorphins that have opiate-like effects
   • 1996, David Foster Wallace, Infinite Jest: A Novel, New York, N.Y.; Boston, Mass.: Little, Brown and Company, →ISBN, page 67:

     Some of the more marginal players start in as early as maybe twelve, I'm sorry to say, particularly 'drines before matches and then enkephaline after […]

• met-enkephalin