Met-enkephalin is an endogenous opioid peptide that acts as an agonist at μ-opioid receptors (μORs) and δ-opioid receptors (δORs). Met-enkephalin exhibits neuromodulatory, antinociceptive/analgesic, antidepressant, and gastrointestinal motility modulating activities. Like other endogenous opioids, met-enkephalin modulates expression of opioid receptors and plays a role in reward/reinforcement signaling. Met-enkephalin is also involved in exercise-induced reversal of neuropathic pain and in animals undergoing the forced swim test, decreases immobility time. Met-enkephalin inhibits gastrointestinal muscle contractility, inhibiting motility and gastric emptying. Additionally, analogs of this peptide display anticancer and antiepileptic/anticonvulsant activities.