LL-37
Cathelicidin (human)
LL-37 (Cathelicidin (human)) is a healing & recovery research compound. Innate-immune antimicrobial peptide — disrupts microbial membranes and modulates inflammation and wound healing.
LL-37 quick facts
| Reported research dose | 100mcg-500mcg |
| Route | Subq |
| Frequency | 3-5x A Week |
| Half-life | Short (minutes-hours) |
| Forms | Injectable |
| Evidence level | In-vitro + animal |
Antimicrobial/biofilm and gut interest. Powerful — can be pro-inflammatory, so it's not a 'more is better' peptide.
How LL-37 works
Innate-immune antimicrobial peptide — disrupts microbial membranes and modulates inflammation and wound healing.
Proposed benefits
Antimicrobial, biofilm and gut-immune support.
Where to get LL-37
Buy LL-37 at Flawless Compounds →Bacteriostatic water is the diluent — sterile water with 0.9% benzyl alcohol, which is what lets a vial be drawn from more than once. It does not come with the vial, and unlike the compound it is bought again every time.
Need bacteriostatic water? Get it at AminoWell USA (my company) → Code CAMERON.
The evidence for LL-37
Graded by what exists behind each claim.
✅ Clinically validated
- Human trials exist and are small — topical LL-37 was studied in hard-to-heal venous leg ulcers in a phase 1/2 trial, which reported improved healing at lower doses and, notably, less benefit at the highest dose. A dose-response that turns over is a real finding, not noise.
📊 Correlative data
- Used in the research community for chronic infection and biofilm-associated conditions. Injection-site reactions are the most consistent report, which the mechanism predicts.
🧪 Theoretical / extrapolated
- The only human cathelicidin — an endogenous antimicrobial peptide that disrupts bacterial membranes directly and also modulates immune signaling and promotes angiogenesis. Vitamin D upregulates its expression, which is one of the better-supported links between vitamin D status and infection.
- Membrane disruption is not selective, which is why high concentrations irritate host tissue too — and the likely explanation for the inverted dose-response in the ulcer trial.
How to read these tiers: they say how much human evidence exists, not how well something works — and ✗ flags harm, never a disappointing trial. How the evidence tiers work →
What LL-37 actually does
LL-37 is the only cathelicidin humans make, and it is not primarily an antibiotic. It is a signaling molecule that happens to be able to kill bacteria. Getting that order right changes every conclusion on this page.
How it is made, which is the part that matters for dosing. The CAMP gene encodes a precursor, hCAP18, that is stored in neutrophil granules and secreted by epithelia. The mature 37-residue peptide is released by proteolytic cleavage of that precursor at the site where it is needed. The body never floods the circulation with free LL-37 — it makes the precursor and cuts it locally. Injecting the mature peptide systemically inverts that design.
The transcriptional switch is vitamin D, and this is unusually direct. The CAMP gene carries a vitamin D response element, so the active form of vitamin D drives its expression; this is the best-characterized route by which vitamin D status feeds into innate antimicrobial defense White 2022. That gives the compound something almost nothing else here has: an endogenous production lever with a cheap blood test attached to it.
What the peptide does to a membrane. It is strongly cationic and amphipathic — it folds into a helix with charged residues on one face and hydrophobic residues on the other. Bacterial membranes are anionic on the outer leaflet; mammalian membranes keep their anionic phospholipids on the inner leaflet and carry cholesterol. That difference in surface charge is the entire basis of selectivity, and it is a selectivity of degree, not of kind: at higher concentrations the same mechanism damages human cells. Selectivity that depends on a concentration window is the defining safety problem of every antimicrobial peptide.
And the immunological job, which is the larger one. LL-37 binds DNA and RNA released from damaged cells, protects those nucleic acids from degradation, and delivers them into endosomal Toll-like receptors of dendritic cells — converting extracellular debris into an interferon-driving signal. It is found in neutrophil extracellular traps, it modulates neovascularization and inflammatory signaling, and it has been reviewed for direct antiviral activity and effects on endothelial repair and islet cell function Aloul 2022. That nucleic-acid-carrying property is why the next section reads the way it does.
Cell, rodent, human — and where it stops
Step one, expression and induction, which is settled. Calcitriol regulates antimicrobial peptide genes including CAMP, and the pathway from vitamin D status to LL-37 expression is the best-worked example of vitamin D acting on innate immunity White 2022.
Step two, and here the direction of the evidence reverses. In psoriasis, serum LL-37 is significantly higher than in healthy volunteers, and it correlates positively with interferon-gamma, interleukin-17 and interleukin-22 (P<.001 for each) across 50 patients and 33 controls, falling after treatment Lao 2023. High LL-37 is a marker of active inflammatory disease, not of good defense.
Step three, the immunological mechanism behind that correlation, measured in people. Citrullinated LL-37 — but not native LL-37 — induced interferon-gamma production by T cells and B cells from psoriasis patients, and interleukin-10 production by their CD4+ T cells. Circulating neutrophil extracellular traps were present in the serum of 40% of patients and 55% of healthy donors, and contained LL-37 in 63% and 27% of those respectively. The high responders to citrullinated LL-37 were the patients who had circulating traps and an earlier age of disease onset Martín Monreal 2023.
Step four, the finding that should stop anyone thinking of this as an injectable. LL-37 is an autoantigen in several autoimmune diseases and in acute coronary syndrome. In patients with acute coronary syndrome, T cells responded to LL-37 with persistence of CD134 and CD137 — markers that impair tolerance and promote memory — and CD8+CD69+CD137+ T cells were significantly increased by LL-37 stimulation compared with controls. Control of that self-reactive response ran predominantly through CTLA-4 Chernomordik 2023.
Step five, the metabolic association, which runs the same way. A narrative review of cathelicidin in metabolic syndrome reports LL-37 linked to adipose tissue inflammation and to the development of insulin resistance in obesity, acting partly through Toll-like receptor activation and pro-inflammatory cytokine secretion, with a negative relationship between LL-37 levels and HDL cholesterol Popa 2024.
The obstacle, stated as bluntly as the evidence allows. There is no human trial of injected LL-37 for anything. The human literature is about endogenous concentrations, and in that literature high LL-37 tracks with psoriasis severity Lao 2023, with impaired self-tolerance in coronary disease Chernomordik 2023, and with insulin resistance and lower HDL Popa 2024. The therapeutic proposals in the literature are about upregulating endogenous expression Aloul 2022, which is a different intervention from injecting the mature peptide.
LL-37 pharmacokinetics — how much of it actually gets in
The card says short, minutes to hours, and gives no number because no human pharmacokinetic study of exogenous LL-37 exists. What can be said is what happens to a 37-residue cation in blood, and it is specific enough to be useful.
Three things degrade or neutralize it, in order of speed. First, plasma and tissue proteases: a linear peptide with free termini is exposed to aminopeptidases and endopeptidases with no protective modification of any kind — no D-amino acids, no cyclization, no fatty acid. Second, and more important, binding: LL-37 is strongly cationic and blood is full of anions. It associates with plasma lipoproteins, with serum albumin and with glycosaminoglycans, and bound peptide is not free peptide. Third, the ionic strength of plasma itself weakens the electrostatic step that drives membrane binding — the salt sensitivity of cationic antimicrobial peptides is why in-vitro potency routinely overstates what happens in serum by an order of magnitude or more.
The lipoprotein interaction is not a footnote here. The human literature reports a negative relationship between LL-37 and HDL cholesterol Popa 2024. Whatever the causal direction, a cationic peptide that partitions onto lipoproteins has a distribution determined by a person's lipid panel, which means the same injected dose does not produce the same free concentration in two different people.
Oral is not a route and the reason is worth being exact about. A 37-residue linear peptide meets pepsin at gastric pH and pancreatic proteases in the duodenum; there is no transporter for it and it is far too large for passive absorption. Anything oral delivering LL-37 activity is delivering fragments, and fragments of an amphipathic helix do not necessarily retain either the antimicrobial or the immunomodulatory function — the two depend on different regions.
The kinetic conclusion that actually changes a decision. Because free peptide is short-lived and mostly bound, a subcutaneous injection produces a high local concentration at the depot and a low systemic one. That is the opposite of the profile implied by the systemic claims made for it — and it means the tissue most exposed to the concentration window where selectivity fails is the skin and subcutis at the injection site.
What would have to be true, and how you would know it was not
Three predictions. The first is the one that would make this compound rational; the third is the one that argues against injecting it at all.
1. Raising vitamin D should raise endogenous LL-37, and that is the cheap version of this intervention. The CAMP gene is under vitamin D control White 2022. Prediction: in a person with a low vitamin D, correcting it into range raises circulating cathelicidin measurably over 8 to 12 weeks, and does so without any of the risks in the safety section. This is falsifiable, the assays exist, and it is the experiment a research-minded person should run before considering the injectable version of the same molecule.
2. hs-CRP should not fall — and if it rises, that is the mechanism, not a bad batch. The human data associate high LL-37 with active inflammation rather than with its resolution: it correlates positively with interferon-gamma, interleukin-17 and interleukin-22 in psoriasis Lao 2023 and with adipose inflammation in metabolic syndrome Popa 2024. Prediction: hs-CRP at baseline and at 8 weeks either does not fall or rises. A page selling this as an anti-inflammatory would predict the opposite; the published human associations do not support that prediction and this one is written to be checkable either way.
3. Against the product: the lipid and autoimmunity predictions. On lipids, the reported inverse relationship with HDL Popa 2024 predicts a measurable fall in HDL on a lipid panel over 12 weeks of exposure — a specific, unwelcome, falsifiable claim. On autoimmunity, LL-37 is an autoantigen in psoriasis and in acute coronary syndrome, where T-cell responses to it show markers that impair tolerance and generate memory Chernomordik 2023, and citrullinated LL-37 drives interferon-gamma responses in a subgroup of psoriasis patients Martín Monreal 2023. Prediction: repeated subcutaneous administration of an autoantigen produces a detectable anti-LL-37 antibody response, and in susceptible people an ANA that was negative becomes positive. Nobody has looked, and it would take one blood draw before and one after.
What nobody has tested yet
Four experiments, none of which requires anything exotic.
Whether injecting it raises the circulating concentration at all. Given plasma binding and salt sensitivity, the free concentration after a subcutaneous dose may be trivially different from baseline. A single time-course of plasma cathelicidin after one injection would establish whether the intervention does anything systemic, and it has never been published.
Whether it becomes citrullinated in vivo. Citrullinated LL-37 is immunogenic where native LL-37 is not Martín Monreal 2023, and peptidylarginine deiminases are released at sites of neutrophil activation — including, plausibly, an irritated injection site. Whether injected LL-37 is modified into its immunogenic form is the single most important unanswered safety question about this compound and nobody has asked it.
Whether upregulating endogenous expression reproduces any of the claimed benefits. The therapeutic hypothesis in the literature is about induction, not injection Aloul 2022White 2022. A trial comparing vitamin D repletion against placebo with cathelicidin and an infection endpoint would test the whole premise, and the infection-endpoint half has been attempted for vitamin D without cathelicidin being measured alongside it.
What the concentration window looks like in human tissue. The selectivity of a cationic amphipathic peptide is a ratio between the concentration that lyses a bacterium and the one that damages a human cell. That ratio has been measured in vitro many times and never in human subcutaneous tissue after an injection, which is the only place it would matter.
LL-37 — its own safety story, not its class's
The specific risk here is not toxicity in the ordinary sense. It is that this molecule is a known human autoantigen and the proposal is to inject it repeatedly.
The autoantigen finding, stated exactly. LL-37 is described in the immunology literature as an autoantigen in several autoimmune diseases and in acute coronary syndrome, with T-cell profiles in patients showing persistence of CD134 and CD137 — markers that impair tolerance and promote memory — and significantly increased CD8+CD69+CD137+ T cells on stimulation Chernomordik 2023. Repeated subcutaneous exposure to a protein antigen is, in immunological terms, an immunization schedule. That is not a rhetorical comparison; it is what subcutaneous repeat dosing of a peptide does.
Psoriasis is the specific contraindication the mechanism names. Serum LL-37 is elevated in psoriasis and correlates with the inflammatory cytokines that drive it Lao 2023, and the citrullinated form provokes interferon-gamma responses in a subgroup of patients with early-onset disease and circulating neutrophil traps Martín Monreal 2023. Anyone with psoriasis, or with a first-degree relative who has it, is being offered more of the molecule their disease is already driven by.
The metabolic direction is unfavorable too. Cathelicidin is linked to adipose inflammation and insulin resistance in obesity and is inversely related to HDL cholesterol Popa 2024. That is the opposite of the direction implied by selling it as a recovery peptide.
What the literature actually proposes, and it is not this. The therapeutic proposals for LL-37 are about upregulating endogenous expression — through vitamin D and related inducers — so the peptide is produced where and when it is needed Aloul 2022White 2022. Endogenous induction and exogenous injection are different interventions with different distribution, different local concentrations and different immunological consequences. Citing the first to justify the second is the central error made about this compound.
Sources read for this page
- Chernomordik F, et al. Impaired tolerance to the autoantigen LL-37 in acute coronary syndrome. Frontiers in Immunology 2023 · PMID 37051254
- Martín Monreal MT, et al. Characterization of circulating extracellular traps and immune responses to citrullinated LL37 in psoriasis. Frontiers in Immunology 2023 · PMID 38173716
- Popa AD, et al. Cathelicidin: Insights into Its Impact on Metabolic Syndrome and Chronic Inflammation. Metabolites 2024 · PMID 39728453
- Lao J, et al. Serum LL-37 and inflammatory cytokines levels in psoriasis. Immunity, Inflammation and Disease 2023 · PMID 36988247
- Aloul KM, et al. Upregulating Human Cathelicidin Antimicrobial Peptide LL-37 Expression May Prevent Severe COVID-19 Inflammatory Responses and Reduce Microthrombosis. Frontiers in Immunology 2022 · PMID 35634307
- White JH. Emerging Roles of Vitamin D-Induced Antimicrobial Peptides in Antiviral Innate Immunity. Nutrients 2022 · PMID 35057465
LL-37 — safety, predicted from mechanism
Predicted from mechanism, not from a human safety trial. How that reasoning works →
What the mechanism predicts
Derived from the molecule, not a trial.
- Repair peptides work by promoting angiogenesis — new blood vessel growth — plus fibroblast migration and growth-factor signaling. That is what makes them useful, and it is the entire basis of the one theoretical concern worth naming: angiogenesis is also what a tumor needs to grow beyond a few millimetres.
- There is no evidence these compounds cause or accelerate cancer. There is a mechanistic reason not to run a pro-angiogenic agent systemically with an active or recently treated malignancy, and that reasoning stands without a trial.
- The second predicted issue is more mundane and more likely: they can mask a signal. Something that reduces pain and inflammation around an injury lets you load a tissue that has not finished healing.
What has actually been reported
- Very well tolerated in reported use. Injection-site reactions and transient light-headedness are the common complaints.
- Human data is thin — most of the literature is rodent — so 'well tolerated' here means 'no signal has emerged from a lot of informal use', which is weaker than a clean trial and stronger than nothing.
How to reduce the risk
Same mechanism as the prediction.
- Stop when the thing you were treating has resolved. There is no mechanism here that demands a clock, and equally no reason to keep running a pro-angiogenic signal once the job is done.
- Do not let reduced pain set your training load. The tissue heals on its own timeline whether or not you can feel it. Reloading early on the strength of feeling better is the most common way people turn a good result into a re-injury.
- Get the diagnosis before the peptide. These accelerate healing of things that heal. A tear that needs surgical repair does not become a tear that does not, and the delay costs you.
- One injury, one compound, long enough to judge it. Otherwise you learn nothing transferable for next time.
What it does to your bloodwork
A fact about the assay.
- Nothing routine tracks these directly. The endpoint is the injury, which means your own honest assessment of function is the measurement.
Don't run this if
- Active or recently treated malignancy — the angiogenesis reasoning.
- Any undiagnosed lump or lesion. Find out what it is first.
The honest unknown
- Long-term systemic exposure in humans has never been characterized. The use case is naturally self-limiting — you stop when the injury resolves — which is why this matters less here than it would elsewhere.
Not medical advice. If you take prescription medication or have a diagnosed condition, check this with a pharmacist or doctor.
LL-37 — interference & stacking
Predicted from mechanism, not from an interaction study. How mechanism-predicted claims are made →
What LL-37 moves on your bloodwork
Expected direction, not a measured one.
- hs-CRP (High-Sensitivity C-Reactive Protein) — ↓ expected to fall
If a repair peptide is doing anything systemic, inflammation is where it would plausibly show.
What to do: Worth a baseline if you are running one for a chronic issue rather than an acute injury. - Comprehensive Metabolic Panel (CMP) — ◆ worth watching
Standard baseline. Nothing in this class predicts a specific abnormality — which is itself worth saying rather than inventing one.
What to do: Annual is fine unless something changes.
The honest position on this class is that the proliferation question is unresolved — anything that accelerates tissue repair is acting on pathways cancer also uses. Nobody has studied it properly either way.
- How to work up to it, and when not to
- When to take it, and why that window
- Cycle length
- Time off between cycles
- Fasted or fed, and when in the day
- Needle gauge and injection site
- Coach Cam's personal notes
- Which compounds push the same lever, and why the dose adds up faster than people count
- What blunts it — the stacks that waste your money
- What compounds the risk, so a side effect arrives sooner than any one of them suggests
- Coach Cam's read on running it alongside the rest of your protocol
Everything above is free and stays free. Skool is where it becomes a plan — LL-37 in an order, with the rest of what you're running.
Unlock in Skool — $10/mo →Bloodwork to run alongside LL-37
Baseline first, then again at 8–12 weeks.
| Marker | What it’s watching for |
|---|---|
| hs-CRP (High-Sensitivity C-Reactive Protein) | Baseline inflammation — the thing you're claiming to reduce |
| Complete Blood Count (CBC) with Differential | Infection, anemia and platelet count before anything injectable |
| Comprehensive Metabolic Panel (CMP) | Liver and kidney baseline |
| Vitamin D (25-Hydroxy) | Low D slows soft-tissue and bone healing measurably |
The Inflammation Deep Dive panel covers these in one order — 10 markers, $248.35 with the discount applied.
Check results you already have → · All 103 markers A–Z
What it is, why it recurs, and where this fits — free to read.
LL-37 — frequently asked questions
What is LL-37?
LL-37 (Cathelicidin (human)) is a healing & recovery research compound. Innate-immune antimicrobial peptide — disrupts microbial membranes and modulates inflammation and wound healing.
Is the full LL-37 protocol on this page?
The reported research dose is on this page, along with how LL-37 works and the evidence behind it. The protocol — how to work up to it, frequency, cycle length, time off, what not to stack it with and Coach Cam's notes — is inside Skool.
What is the half-life of LL-37?
LL-37 has an approximate half-life of Short (minutes-hours), which is part of what determines how often it's dosed.
What's the evidence behind LL-37?
Current evidence level: In-vitro + animal. LL-37 is offered for research purposes only and is not an approved medicine.
What LL-37 is used for
LL-37 appears under 3 goals in the goal router.
Related Healing & Recovery compounds
Where this goes next
The pages here are the frameworks. The protocols — the dosing, the order to correct things in, the week-by-week schedule and what to retest — are inside Skool.