enkephalinase inhibitor enkephalinase inhibitor an enkephalinase inhibitor is a type of enzyme inhibitor which inhibits one or more members of the enkephalinase class of enzymes that break down the endogenous enkephalin opioid peptides. examples include racecadotril, ubenimex (bestatin), rb-101, and d-phenylalanine, as well as the endogenous opioid peptides opiorphin and spinorphin. it also includes rb-3007, semax and selank. analgesic, anticraving, antidepressant, anxiolytic, and antidiarrheal effects are common properties of enkephalinase inhibitors.