What it is
LL-37 is an antimicrobial peptide of 37 amino acids that your body makes. The name is descriptive rather than commercial: two leucine residues at the start, thirty-seven residues in total.
It is released from a precursor protein called hCAP-18, and it is the only cathelicidin in the human genome — a point worth pausing on, because other mammals carry several. Humans have one, and this is it. It is produced by neutrophils, the white blood cells that arrive first at an infection, and by the epithelial linings of the skin, the airways and the gut.
What it does splits neatly in two:
- It kills microbes directly by disrupting their outer membranes. That is a physical mechanism rather than a biochemical target, which is part of why resistance to it is difficult for bacteria to develop.
- It signals. It recruits immune cells, shapes inflammatory responses and takes part in wound repair.
The shape of the evidence
| Measure | LL-37 |
|---|---|
| PubMed title/abstract records | 2,527 |
| Of those, tagged for humans | 1,827 |
| Wider cathelicidin literature | 3,089 |
| Registrations on ClinicalTrials.gov | 20 |
| Of those, interventional | 10 |
| Observational, and therefore phase-less | 10 |
| Commercial sponsors among them | 0 |
| US drug-label records | 0 |
Two of those rows are unusual enough to be the reason this entry is worth reading.
Seven in ten papers are human
For most compounds in this library, the literature is overwhelmingly animal and cell work, and the human fraction is small. Here it is roughly seven in ten. LL-37 is studied in people because it is in people — it can be measured in blood, in sputum, in skin and in gut tissue, in anyone, without giving them anything.
That is also the catch. A human-tagged paper is not a trial of a treatment. Most of this literature asks how much LL-37 a person has and what that correlates with, which is a question about the body rather than about a product.
Not one commercial sponsor
The 20 registered studies — 10 interventional, 10 observational — have lead sponsors including Emory University, the University of California San Diego, Kırıkkale University, the Atlanta VA Medical Center, the International Centre for Diarrhoeal Disease Research in Bangladesh, and the University of Missouri Kansas City.
There is no pharmaceutical company anywhere on the list. This library normally reports the opposite problem — our survodutide entry found 25 of 26 registrations from a single manufacturer, and our cagrilintide entry found all 43 from one. LL-37 has the cleanest independence of anything here and the least commercial momentum, and those are the same fact seen from two sides. Independent research is harder to bend toward a conclusion; it is also not funded to build a product.
The 10 records that list no phase at all are precisely the 10 observational ones. A study that administers nothing has no phase to declare, so the registry says the same thing the literature does: this field measures the peptide far more often than it gives it.
Why nobody has made it into a medicine
The obstacles are specific and worth stating, because "the body makes it, so it must be safe to give" is the assumption this entry exists to complicate:
- Membrane disruption is not selective. The mechanism that punctures bacterial membranes does not perfectly distinguish them from human cell membranes. The therapeutic margin is narrow.
- It is degraded quickly by the body's own enzymes.
- It is sensitive to its surroundings — salt concentration and blood proteins both interfere with its activity, so what works in a dish may not work in a person.
None of that makes it useless; a good deal of research aims at engineered analogues that keep the antimicrobial action and lose the toxicity. It does mean that the peptide as sold is the version with the problems, not the version that solves them.
The intervention that is actually studied
A substantial slice of the human LL-37 literature is not about giving the peptide. Vitamin D switches on the gene that produces it — one of the more clearly established links between a nutrient and a defined immune mechanism — and short-chain fatty acids such as butyrate do something similar in the gut.
So a large part of the research asks whether raising the body's own LL-37 production changes outcomes in infection or inflammation. That is a real question with real trials behind it, and it is a different intervention from injecting the peptide. A page that cites the vitamin D literature as evidence for an LL-37 vial is citing studies of something else.
What is actually sold
Lyophilised LL-37 powder from research suppliers, for reconstitution, and compounded preparations including nasal and nebulised forms — marketed for immune support, gut health, wound healing and persistent infections.
For a contrast worth drawing, the erythropoietin-derived peptide cibinetide occupies the position this compound does not: four registered trials, one of them randomized, placebo-controlled and with its results posted for anyone to read.
No approved label exists for any of it. The human literature is genuine and large, and most of it measures a peptide rather than testing a product. Our entry on how to read this library sets out that distinction, and our VIP entry documents the same gap in a different peptide the body makes for itself.