Pain · Research Phase
Leu-Enkephalin
No lawful US pathway
01 · Overview
Leu-enkephalin is a pentapeptide (Tyr-Gly-Gly-Phe-Leu) identified in 1975 as one of the two enkephalins, natural ligands for opiate receptors (PMID 1207728). Enkephalins are regarded as the endogenous agonists of the delta-opioid receptor (PMID 9087409), although they also bind mu receptors.
It is derived from the precursor proenkephalin and is widely distributed in the central and peripheral nervous systems. In human plasma, leu-enkephalin is rapidly and completely broken down by aminopeptidase, mostly within 30 minutes in laboratory incubations (PMID 11317167).
02 · Research summary & key findings
In rodents, protecting endogenous enkephalins from breakdown with a mixed peptidase inhibitor produced naloxone-reversible analgesia across several pain tests (PMID 2032557). In a rat model of postoperative pain, squalene nanoparticles that shield leu-enkephalin from metabolism reduced mechanical and thermal hyperalgesia (PMID 39019085). Dual inhibitors of the two main enkephalin-degrading enzymes, neprilysin and aminopeptidase N, have shown analgesia in animal models and in preliminary human trials (PMID 29722031). Native leu-enkephalin has not been developed as a drug because of its rapid metabolism.
03 · Regulatory status
Leu-Enkephalin is in the research phase with limited clinical data in humans. Current evidence is primarily derived from preclinical (animal or in vitro) studies.
No lawful pathway today
Leu-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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Leu-Enkephalin is a research 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]Degradation kinetics of leucine5-enkephalin by plasma samples from healthy controls and various patient populations: in vitro drug effects Am J Ther, 2000. PMID 11317167
- [2]Identification of two related pentapeptides from the brain with potent opiate agonist activity Nature, 1975. PMID 1207728
- [3]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
- [4]Indirect-acting strategy of opioid action instead of direct receptor activation: dual-acting enkephalinase inhibitors (DENKIs) J Clin Pharm Ther, 2018. PMID 29722031
- [5]A nanomedicine approach for the treatment of long-lasting pain J Control Release, 2024. PMID 39019085
- [6]A potent and selective endogenous agonist for the mu-opiate receptor Nature, 1997. PMID 9087409
Primary literature
- PubMed: "Leu-Enkephalin"
Peer-reviewed literature indexed by the National Library of Medicine.
- ClinicalTrials.gov: "Leu-Enkephalin"
Registered interventional and observational studies, including status and phase.
- PubChem: "Leu-Enkephalin"
Chemical structure, molecular properties, and bioactivity data.
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