Met-Enkephalin, also called opioid growth factor (OGF), is a naturally occurring endogenous opioid peptide that has opioid effects of a relatively short duration. It is one of the two forms of enkephalin with Leu-enkephalin. Enkephalins are considered the primary endogenous ligands of the delta-opioid receptor, due to their high potency and selectivity for the site over other endogenous opioids. The Met-Enkephalin Peptide competes with and mimics the effects of opiate drugs. The Met-Enkephalin Amide Peptide also serves as a growth factor on certain cells.H-Tyr-Gly-Gly-Phe-Met-NH2 or H-YGGFM-NH2