LL-37
Human Cathelicidin Antimicrobial Peptide
Evidence grade 2 of 5, Thin. Read how the Atlas grades evidence.
LL-37 is the body's own cathelicidin peptide with a very large preclinical literature (antimicrobial, anti-biofilm, wound-healing, immunomodulatory), but human evidence is early. Topical LL-37 showed a signal in a small Phase I/IIa venous-leg-ulcer RCT (Grönberg 2014, n=34) and a small diabetic-foot-ulcer RCT (n=25, 2023), while the Phase IIb HEAL trial (n=148) missed its overall endpoint and was positive only in a large-wound subgroup; intratumoral use in melanoma is a single registered Phase I study (NCT02225366). No systemic product is approved, and its role in cancer is genuinely double-edged (pro-tumor in ovarian, lung, breast; anti-tumor in colon, gastric), so grade 2 reflects preliminary human data rather than the grade 3 currently on the entry.
Counted on the record: 3 human studies, 0 animal studies, 0 lab studies.
The database supports competing human-trial and participant totals. No editorial choice is made in this migration.
- FDA
- No FDA-approved LL-37 product; human use is limited to early-phase investigational trials (topical chronic-wound RCTs and a Phase I intratumoral melanoma study). Injectable and gray-market 'research chemical' LL-37 is unapproved for human use.
- WADA
- Not prohibited
Reference only. Not medical advice.
What can go wrong
Endogenous but pro-inflammatory and cytotoxic at higher concentrations; poor proteolytic stability limits systemic use, and its role in cancer is double-edged (pro-tumor in some tissues, anti-tumor in others), so unapproved injectable use carries uncharacterized risk.
Talk to a clinician before taking this, particularly if you have any history of cancer. The Atlas can tell you what has been studied about LL-37. It cannot tell you how it would interact with your body, your history, or anything else you are taking, and nothing on this page is a reason to start.
The only cathelicidin in humans, found in neutrophils, skin, and the respiratory tract. A broad-spectrum antimicrobial that is also anti-inflammatory, anti-biofilm, and pro-wound-healing, with growing interest for antibiotic-resistant infections and inflammatory skin conditions.
The body's own antibiotic. In neutrophils and skin. Anti-cancer signals emerging.
What people take it for
These are the reasons people give for taking it. They are not effects it has been shown to have.
How it is supposed to work
LL-37 is the body’s own broad-spectrum antibiotic, the single human member of a family of natural defense peptides. Because it carries a positive charge, it is drawn to the negatively-charged surfaces of bacteria, where its helical shape inserts into and tears open the microbe’s membrane, killing it directly. It also does much more: it neutralizes bacterial toxins, breaks up biofilms, summons immune cells to infection sites, and helps wounds heal. The gray-market pitch is to inject extra LL-37 to harness all of that, on the theory that more of a natural defender must be better.
- Step 1Membrane attackIts positive charge draws it to bacterial surfaces, where its helix opens the microbe's membrane.
- Step 2Toxins and biofilmsIt neutralises bacterial toxins and breaks up biofilms.
- Step 3Immune signallingIt summons immune cells to an infection site and helps wounds heal.
- Step 4Tissue dependenceIts effects differ by tissue, so antimicrobial activity alone predicts little about benefit.
Thirty-seven amino acids in a cationic helix.
- Type
- Human cathelicidin peptide
- Action
- Membrane-disrupting antimicrobial
- Also
- Immune signaling, wound healing
- Nature
- Double-edged
- Human safety data
- None (injectable)
- Approved
- No
The Body’s Own Antibiotic, With A Double Edge
LL-37 is genuinely important and well-studied, a cornerstone of innate immunity with broad antimicrobial, immune-signaling and wound-healing activity, and it is a serious research lead precisely because its membrane-disrupting mechanism makes bacterial resistance slower to develop than with conventional antibiotics. That is the appealing half. The honest other half is that LL-37 is double-edged. The same peptide that fights infection also drives inflammatory disease when present in excess: it is a known contributor to rosacea and psoriasis, it can act as an autoantigen that provokes autoimmune responses, and it is cytotoxic to human cells, with ambiguous, context-dependent effects in cancer. There are no approved LL-37 drugs and, as of 2026, no long-term human safety data for injecting it. So injecting extra of a membrane-disrupting, immune-activating, potentially-autoimmune peptide is not obviously beneficial and is plausibly risky, the opposite of the more-is-better pitch.
How it is taken
Topical
topical aqueous solution Synthetic LL-37 acetate in an aqueous solution; the phase IIb trial used 0.5 or 1.6 mg/mL. The trial and patent do not provide a general consumer shelf life or support injectable use. Randomized venous-leg-ulcer trials with controlled application to wounds.
Topical
cream LL-37 in a cream used on diabetic foot ulcers. The publication does not establish storage stability for other LL-37 forms. Small randomized double-blind diabetic-foot-ulcer study.
Injection
Recorded because this entry documents injectable use. The Atlas holds no vial, reconstitution or storage detail for it.
Safety in detail
- LL-37 damages human cells at higher concentrations, which matters for whole-body use.
- Its effects in cancer run both ways depending on the tissue, so the picture stays unresolved.
Children and teenagers
LL-37 as an injectable is unapproved, cytotoxic and potentially autoimmune, with no human safety data, which makes it inappropriate for minors. Any pediatric infection or immune problem belongs with physicians using approved treatments. There is no appropriate pediatric use.
What people get wrong
Often saidA natural human antimicrobial peptide must be safe to inject
ActuallyHuman LL-37 trials have used controlled topical or intratumoral settings. That does not establish the safety of systemic or gray-market injection, and LL-37 can also affect human cells and inflammatory signaling.
Often saidLL-37 is simply a broad-spectrum antibiotic
ActuallyLL-37 also changes immune signaling, wound repair, and cell growth. Its effects can differ by tissue, which is why antimicrobial activity alone does not predict overall benefit or safety.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
LL-37’s money runs through gray-market peptide vendors selling it as an injectable for infections, gut health, healing and immune support, alongside research-reagent suppliers and a real pharmaceutical interest in antimicrobial-peptide drug development. There is no approved product. The marketing leans on genuine innate-immunity biology to sell an injectable that biology does not actually endorse.
How we got here
LL-37 is a natural human peptide, not a designed drug: the CAMP gene encodes an 18 kDa precursor (hCAP18) whose C-terminal fragment is proteolytically released as the mature 37-residue peptide, named LL-37 for its two leading leucines and length. It was first characterized in the 1990s (early work described the FALL-39 form) and is the sole cathelicidin found in humans. Therapeutic development has centered on topical formulations for chronic wounds through Swedish groups and companies, plus an academic intratumoral melanoma program, while a separate wave of vendors now sells synthetic LL-37 as an injectable research chemical for immune and antimicrobial claims that regulators have not approved.
Cathelicidins were identified as innate-immunity antimicrobial peptides, and LL-37 was characterized as the sole human cathelicidin. Extensive research mapped its membrane-disrupting antimicrobial action, its immune-signaling and wound-healing roles, and its double-edged contributions to rosacea, psoriasis, autoimmunity and host-cell toxicity. Strong interest in it as an anti-resistance antimicrobial lead grew alongside a gray-market injectable use among biohackers and chronic-infection sufferers, well ahead of any human safety data.
Human wound trials
2014 to 2023
Topical LL-37 has reached randomized wound studies with mixed results.
- 2014Topical LL-37 is tested in venous leg ulcersLower-dose topical LL-37 improved early healing measures in a small trial. The result does not support systemic injection.
- 2022The larger venous-ulcer trial is negative overallLL-37 did not improve healing across the full trial population. A larger-ulcer subgroup signal was identified only after the main analysis.
- 2023LL-37 cream improves granulation in a small studyThe cream improved granulation but did not reduce measured inflammation or bacterial colonization.
The numbers behind the grade
- Type
- Human cathelicidin
- Action
- Membrane-disrupting
- Also
- Immune, wound healing
- Nature
- Double-edged
- Human data
- None (injectable)
- Approved
- No
The people taking it
Users are biohackers and people with long-running infections, drawn by the idea of a natural antibiotic, alongside people seeking immune support and faster wound healing.
The only human cathelicidin, a real broad-spectrum antimicrobial and immune peptide and a serious research lead, sold gray-market as an injectable despite no human safety data and a genuinely double-edged biology.
LL-37’s users are biohackers and people with chronic infections, drawn by the natural-antibiotic concept, along with gut-health and immune-support users, wound-healing and recovery seekers, and people worried about antibiotic resistance. It attracts self-experimenters and the chronically ill willing to act ahead of evidence.
A real innate-immunity peptide and research lead for anti-resistance antimicrobials and wound healing, sold gray-market as an injectable for infections, gut health, healing and immune support, with no human safety data and double-edged risk. Not approved.
Set against the alternatives
Against conventional antibiotics, LL-37 is appealing because its physical, membrane-disrupting mechanism makes resistance slower to emerge, a real draw amid the antibiotic-resistance crisis, but conventional antibiotics are proven and approved while injectable LL-37 is not. Against defensins, the other class of human antimicrobial peptides, LL-37 is structurally different, cysteine-free and helical rather than pore-forming, and the two are complementary parts of innate immunity. And against healing peptides like BPC-157 and TB-500, LL-37 shares wound-healing claims but adds an antimicrobial and immune role and a sharper double-edged risk. Its strength is being a serious anti-resistance research lead; its weakness is that injecting it is unproven and biologically two-edged.
What we do not know
- Whether engineered cathelicidin-based drugs can become safe, approved antimicrobials.
- Whether injecting LL-37 helps or harms, given no human data and double-edged biology.
- How to manage its host-cell toxicity, autoimmune potential and cancer ambiguity.
- Whether the vitamin-D-to-LL-37 axis offers a safer way to modulate it.
What could change
Antimicrobial drug developmentEngineered cathelicidins are explored as anti-resistance antibiotics.Vitamin-D axisThe vitamin-D-to-LL-37 link is studied as a modulation route.Double-edged researchIts roles in inflammation, autoimmunity and cancer are actively investigated.Gray-market persistenceInjectable use continues ahead of the evidence.
Legal status
LL-37 is not approved and has no human safety or efficacy data for injectable use. Research-grade material is sold explicitly for laboratory use, not for patients, while gray-market injectable LL-37 is marketed for infections, healing and immune support. Its double-edged biology is a real concern.
Status current as of July 2026. Regulatory positions change, sometimes quickly.
The market for this
What follows describes how this is bought and sold. It is not a buying guide and it is not an endorsement of any seller.
Available only through gray-market research vendors, which is not a human-use route and offers no human safety data, while the peptide is cytotoxic and potentially autoimmune. There is no legitimate route. The antimicrobial-peptide concept is a real research lead, but injecting LL-37 is unvalidated and mechanistically risky, and infections should be treated by a physician with approved options.
Gray-market injectable LL-37 is moderately priced, with research-grade material more expensive. The cost buys an untested and biologically risky compound rather than a validated therapy.
Synthesized overseas, mainly in China, as gray-market injectable or research-use-only material of variable quality, with no safety assurance for human use.
China and research vendorsSupply gray-market injectable LL-37 and research-use-only material.Research reagentsLL-37 is sold to laboratories for study, explicitly not for patients.Pharmaceutical pipelinesAntimicrobial-peptide drug development remains early and preclinical.
At a glance
- Class
- Only human cathelicidin
- Found in
- Neutrophils, skin, lungs
- Action
- Broad-spectrum antimicrobial
- Interest
- Antibiotic resistance
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about LL-37.
Nothing outstanding on this one.
Sources
Topical LL-37 was safe and enhanced healing in hard-to-heal venous leg ulcers in a randomized placebo-controlled Phase I/IIa trial (n=34), with lower doses outperforming placebo
LL-37 cream significantly improved granulation in diabetic foot ulcers versus placebo in a randomized double-blind controlled trial (n=25)
Intratumoral LL-37 (LL37) in cutaneous/subcutaneous melanoma metastases is a single registered Phase I study; weekly intratumoral injections for up to 8 weeks, not an approved therapy
LL-37 has a double-edged role in cancer: overexpression promotes ovarian, lung and breast cancers while suppressing colon and gastric tumorigenesis; effects are tissue-specific and receptor-dependent
hCAP18/LL-37 promotes cell proliferation and can suppress the antitumor activity of active vitamin D in hepatocellular carcinoma, illustrating a pro-tumor mechanism
Cathelicidin hCAP18/LL-37 promotes cell proliferation in hepatocellular carcinoma, PMC (2022)
LL-37 is the C-terminal fragment of the hCAP18 precursor encoded by the human CAMP gene, the only cathelicidin in humans, expressed in neutrophils, skin and respiratory epithelium
Cathelicidin antimicrobial peptide, Wikipedia (identity/gene summary)
CAMP gene transcription is directly induced by 1,25-dihydroxyvitamin D via a vitamin D response element, linking circulating hCAP18/LL-37 to vitamin D status
Positive correlation between circulating hCAP18/LL-37 and 25-hydroxyvitamin D, PMC (2013)
Recent review of the cathelicidin family notes LL-37's broad antimicrobial and immunomodulatory activity but flags low proteolytic stability, cytotoxicity and production cost as barriers to systemic clinical use
The human cathelicidin peptide LL-37 inhibits pancreatic cancer growth by suppressing autophagy and reprogramming the tumor immune microenvironment, an anti-tumor example
The studies that matter
Antimicrobial mechanismestablished
LL-37 kills a broad range of microbes by disrupting their membranes, a physical mechanism that slows resistance compared with conventional antibiotics.
Immune signaling2000
A landmark study showed LL-37 recruits neutrophils, monocytes and T cells, bridging innate antimicrobial defense and adaptive immunity.
Wound healingestablished
LL-37 promotes wound healing, angiogenesis and cell migration beyond its direct killing.
Double-edged biologydocumented
Excess LL-37 in skin contributes to rosacea and psoriasis and can act as an autoantigen, and the peptide is cytotoxic to host cells.
Injectable safety2026
No long-term human safety data exist for injectable LL-37, and there are no approved products.