Pain · Investigational
Met-Enkephalin
No lawful US pathway
01 · Overview
Met-enkephalin is a pentapeptide (Tyr-Gly-Gly-Phe-Met) that differs from leu-enkephalin only in its C-terminal amino acid (PMID 1207728). Enkephalins are regarded as endogenous agonists of the delta-opioid receptor (PMID 9087409), and met-enkephalin also binds mu receptors.
Derived from proenkephalin, it is involved in pain modulation and stress responses, and, under the name opioid growth factor, it acts through its own receptor to slow cell proliferation (PMID 24605021). It is rapidly degraded by enkephalinases, mainly neprilysin and aminopeptidase N (PMID 29722031).
02 · Research summary & key findings
In rodents, enkephalins protected from enzymatic breakdown produced analgesia in a range of morphine-sensitive pain tests (PMID 2032557). As opioid growth factor, met-enkephalin inhibited pancreatic cancer growth in cell culture and in mice, which led to phase I and II trials (PMID 24605021). In an open-label phase II trial in 24 patients with advanced pancreatic cancer after failed chemotherapy, weekly intravenous opioid growth factor was well tolerated, and survival was longer than in untreated historical controls (PMID 20890374). These results come from uncontrolled studies and have not led to approval.
03 · Regulatory status
Met-Enkephalin is in the investigational stage. While preclinical and early-phase data exist, it has not received regulatory approval for clinical use in the United States.
No lawful pathway today
Met-Enkephalin is not FDA-approved and does not currently have a lawful prescription or compounding pathway in the United States, so we do not sell it and will not book a consultation for it. That can change: in 2026 FDA began reviewing several peptides for compounding. If you are working on the goal it is studied for, a licensed clinician can tell you what is lawfully available, which may be something else.
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Met-Enkephalin is an investigational compound, is not FDA-approved, and has no lawful US compounding pathway, so we do not offer it and no clinician we work with will prescribe it. Products sold online as “research chemicals” are not made or tested to the standards required of medicines. If you are working on injury recovery and tissue repair, a licensed clinician can tell you at a free consultation whether an FDA-approved or lawfully compounded treatment fits you, or whether nothing does.
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04 · Administration routes
- Endogenous peptide
References
- [1]Identification of two related pentapeptides from the brain with potent opiate agonist activity Nature, 1975. PMID 1207728
- [2]Analgesic responses elicited by endogenous enkephalins (protected by mixed peptidase inhibitors) in a variety of morphine-sensitive noxious tests Eur J Pharmacol, 1991. PMID 2032557
- [3]Opioid growth factor improves clinical benefit and survival in patients with advanced pancreatic cancer Open Access J Clin Trials, 2010. PMID 20890374
- [4]Opioid growth factor and the treatment of human pancreatic cancer: a review World J Gastroenterol, 2014. PMID 24605021
- [5]Indirect-acting strategy of opioid action instead of direct receptor activation: dual-acting enkephalinase inhibitors (DENKIs) J Clin Pharm Ther, 2018. PMID 29722031
- [6]A potent and selective endogenous agonist for the mu-opiate receptor Nature, 1997. PMID 9087409
Primary literature
- PubMed: "Met-Enkephalin"
Peer-reviewed literature indexed by the National Library of Medicine.
- ClinicalTrials.gov: "Met-Enkephalin"
Registered interventional and observational studies, including status and phase.
- PubChem: "Met-Enkephalin"
Chemical structure, molecular properties, and bioactivity data.
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