Endomorphin-2 (EM-2) is an endogenous opioid peptide and one of the two endomorphins (EM-1 and EM-2). Endomorphin-2 is a potent agonist for mu-opioid receptors. EM-2 is a potent analgesic having high affinity (Ki = 690 pM) and selectivity for mu-opioid receptors. EM-2 produces analgesia in animals as equipotent as morphine. H-Tyr-Pro-Phe-Phe-NH2 or H-YPFF-NH2