Section 01
What it's used for
Fighting drug-resistant bacteria
Researchers are developing LL-37-based drugs to fight bacteria that resist normal antibiotics, such as MRSA and VRE. It works by breaking apart bacterial membranes, a method these bacteria have no defense against.
▸Clinical wording
LL-37 and its analogs are being developed as novel antimicrobials against multidrug-resistant (MDR) bacteria including MRSA, VRE, and carbapenem-resistant Enterobacteriaceae. Its membrane-disrupting mechanism is fundamentally resistant to the resistance mechanisms that defeat conventional antibiotics.
Healing hard-to-treat wounds
In placebo-controlled human trials, LL-37 applied to skin improved healing of venous leg ulcers. For diabetic foot ulcers, only observational studies exist, showing altered LL-37 levels in wound tissue — no treatment trial has been done.
▸Clinical wording
LL-37 has been tested in placebo-controlled human clinical trials specifically for hard-to-heal venous leg ulcers, where topical LL-37 improved wound healing. For diabetic foot ulcers, the published literature is limited to observational studies showing altered LL-37 expression in ulcer tissue, not therapeutic trials, and no clinical trial of LL-37 for diabetic ulcers or pressure sores has been found. Impaired innate immunity and biofilm formation are proposed as general mechanisms behind non-healing wounds.
Breaking through bacterial biofilms
LL-37 is being studied for biofilm infections — where bacteria form a protective coating on artificial joints, catheters, and chronic wounds — because regular antibiotics often cannot penetrate this layer to reach them.
▸Clinical wording
LL-37's unique anti-biofilm properties make it a candidate for treating biofilm-associated infections in prosthetic joints, catheters, and chronic wounds where conventional antibiotics fail to penetrate biofilm matrices.
Role in inflammatory diseases
Researchers are studying how LL-37 activity contributes to rosacea, psoriasis, artery hardening (atherosclerosis), and inflammatory bowel disease, hoping to find new treatment strategies by understanding its regulation.
▸Clinical wording
Research explores LL-37 modulation in rosacea (where LL-37 overexpression contributes to pathology), psoriasis, atherosclerosis, and inflammatory bowel disease. Understanding LL-37 regulation may yield therapeutic strategies for these conditions.
Cancer research, mixed signals
In lab cell studies, LL-37 slowed growth of stomach and colon cancer cells (the colon result used a modified version, not the natural peptide). In ovarian cancer cells, published studies found the opposite: LL-37 promoted cancer growth.
▸Clinical wording
In cell-culture studies, LL-37 has shown anti-proliferative activity against gastric and colon cancer cells, though the colon evidence used an LL-37 analogue rather than the native peptide, and in gastric cancer cells the effect involves activation of bone morphogenetic protein signaling via proteasome inhibition rather than membrane disruption. In ovarian cancer, published studies report the opposite effect: LL-37 promotes rather than kills ovarian cancer cells, contradicting any claim of selective cytotoxicity there. These findings come from in vitro cell-culture models; no anti-tumor immune-response data were identified in the cited sources.
Defense against lung infections
LL-37 plays a role in the lung's natural defenses, making it a research candidate for pneumonia and other respiratory infections — particularly in immunocompromised patients who produce less of this natural peptide.
▸Clinical wording
LL-37's role in lung innate defense makes it a candidate for treating pneumonia and respiratory infections, particularly in immunocompromised patients with reduced cathelicidin expression.
Section 02
Mechanism of Action
Tearing holes in bacterial walls
- The molecule carries a positive charge that pulls it onto the negatively charged surface of bacteria.
- Once attached it slips into the fatty membrane and punches pores or strips it apart.
- The damaged membrane leaks, loses its electrical balance, and the microbe dies.
▸Clinical wording
Membrane Disruption (Antimicrobial)
LL-37 kills microorganisms through direct interaction with their cell membranes. Its cationic (+6 charge at physiological pH) and amphipathic alpha-helical structure enables electrostatic attraction to negatively charged bacterial membranes (rich in phosphatidylglycerol and lipopolysaccharide). Upon binding, LL-37 inserts into the lipid bilayer, forming toroidal pores or carpet-like disruptions that cause membrane depolarization, osmotic imbalance, and cell death.
Breaking up bacterial slime layers
- Bacteria build protective slime communities called biofilms, and this molecule is among the strongest natural disruptors known.
- At doses too low to kill, it jams the chemical chatter bacteria use to organise.
- It keeps bacteria twitching and unable to settle, and can also break into existing biofilms.
▸Clinical wording
Anti-Biofilm Activity
LL-37 is one of the most potent natural anti-biofilm agents known. At sub-antimicrobial concentrations, it prevents biofilm formation by interfering with quorum sensing, downregulating biofilm-related genes, and promoting twitching motility that prevents bacterial attachment. It can also penetrate and disrupt established biofilms.
Calling immune cells to infection
- It flips a switch on immune cells (formyl peptide receptor 2) that acts as a homing signal.
- Several kinds of white blood cell then travel toward the site of infection.
- The same switch tunes inflammatory messengers, boosting defence while holding excess inflammation back.
▸Clinical wording
Immunomodulation via Formyl Peptide Receptor 2
LL-37 activates the formyl peptide receptor 2 (FPR2/FPRL1) on immune cells, triggering chemotaxis of neutrophils, monocytes, and T-cells to infection sites. FPR2 activation also modulates cytokine production — enhancing anti-pathogen responses while limiting excessive inflammation.
Several routes to closing wounds
- Skin surface cells are pushed to multiply and crawl across the wound.
- A vessel-growth signal (VEGF) rises, so new blood vessels form in the healing area.
- A growth-factor pathway in skin cells is switched on and repair stem cells are drawn in.
▸Clinical wording
Wound Healing Promotion
LL-37 promotes wound healing through multiple mechanisms: stimulation of epithelial cell migration and proliferation, induction of angiogenesis via VEGF upregulation, and activation of the EGFR/STAT3 signaling pathway in keratinocytes. It also recruits mesenchymal stem cells to wound sites.
Mopping up bacterial toxin
- Gram-negative bacteria carry a toxin (lipopolysaccharide) that the immune system reads as a danger alarm.
- The molecule grabs that toxin directly and stops the alarm receptor from firing.
- This anti-toxin action can guard against blood poisoning and runaway inflammatory responses.
▸Clinical wording
LPS Neutralization
LL-37 directly binds and neutralizes lipopolysaccharide (LPS/endotoxin) from Gram-negative bacteria, preventing TLR4-mediated inflammatory signaling. This anti-endotoxin activity can protect against septic shock and excessive inflammatory responses to bacterial infection.
Section 03
Biological Pathways
- Membrane DisruptionLL-37's cationic, amphipathic alpha-helix binds anionic bacterial membranes and inserts into the bilayer, forming toroidal pores that depolarize the membrane, causing osmotic collapse and cell death.
- Anti-Biofilm ActivityAt sub-antimicrobial concentrations LL-37 blocks biofilm formation by interfering with quorum sensing and biofilm genes and promoting twitching motility, and can also penetrate biofilms already established.
- FPR2 ImmunomodulationLL-37 activates formyl peptide receptor 2 on immune cells, driving chemotaxis of neutrophils, monocytes, and T-cells to infection sites while shaping cytokine output toward clearance over excess inflammation.
- EGFR/STAT3 Wound RepairMetalloproteinase-released EGFR ligands let LL-37 transactivate EGFR in keratinocytes; downstream STAT3 signaling, VEGF-driven angiogenesis, and stem cell recruitment drive epithelial migration and wound closure.
Section 04
Dosage Information
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES| Route / system | Context | Range studied | Limitation |
|---|---|---|---|
| Topical — venous leg ulcers | Phase 1/2 and phase 2b, hard-to-heal ulcers | 0.5, 1.6 and 3.2 mg/mL, 25 µL per cm² of ulcer — 12.5, 40 and 80 µg per cm² — twice weekly; four weeks in 34 patients, thirteen in 144 | It kills human cells above about 1–10 µM, so the hunt was for a ceiling, not a higher dose: 3.2 mg/mL killed ulcer tissue, the lower two missed wound closure. |
| Topical — diabetic foot ulcers | Randomised trial, 25 patients, mildly infected wounds | 0.5 mg of LL-37 per gram of cream, 0.025 mL per cm² of wound, twice weekly for four weeks — eight applications in all | It moved a granulation score and nothing else: wound area, the inflammation markers IL-1α and TNF-α, and bacterial counts matched placebo. |
| Injected into tumours | Phase 1/2 in metastatic melanoma, closed with 4 patients | 250 µg per tumour, raised to 500 µg in the second group, into two to four skin or under-skin lesions weekly for up to eight weeks | Four people in total, so the study fixes neither a dose nor an effect. The peptide went into tumour tissue — not where anyone injecting at home puts it. |
| Subcutaneous — self-administration | Circulating practice outside any trial | 100–250 µg a day, up to 500 µg — about 1–7 µg/kg at 70–90 kg; five days a week for two to four weeks, then an equal break | Circulating practice, not a finding: no trial has ever injected LL-37 to act throughout the body. Every human dose on record went onto a wound or into a tumour. |
Results
Syringe Fill Level (100u syringe)
Set positive values for: Recommended dose per kg.
Research Use Only. This information is for educational and research purposes only. Not intended for medical advice or self-medication.
Section 05
Protocols
- Protocol 01
LL-37 Antimicrobial Protocol
Natural antimicrobial peptide for immune support, wound healing, and gut repair.
- Focus
- Immune Support
- Level
- Intermediate
- Duration
- 10 weeks
Section 06
Stability & Storage
Lyophilised powder
Supplied as a white lyophilised powder, kept at -20°C for long-term stability (12-18 months) or at 2-8°C for up to 3 months. In biological fluids the peptide is moderately susceptible to breakdown by proteases.
After reconstitution
Reconstituted with sterile or bacteriostatic water into a solution that should stay clear; it is kept at 2-8°C and used within 14 days. Concentrations are kept below 1 mg/mL, since LL-37 tends to aggregate into oligomers at higher levels.
Section 07
Side Effects & Precautions
LL-37's safety picture is built on limited human testing, and the effects below depend on concentration, dose, or route of administration.
How little human data exists
LL-37 has undergone limited clinical testing; most safety data comes from Phase 1/2 clinical trials for wound healing, using topical and local administration.
Local tissue and cell reactions
- At high concentrations, LL-37 can cause local tissue irritation because of its membrane-active properties (it can disrupt cell membranes).
- Toxicity to mammalian cells occurs at concentrations 5-10 times higher than antimicrobial concentrations.
- LL-37 can activate mast cells (immune cells that release histamine) by binding the MrgX2 receptor, causing localized redness and itching.
- This effect is concentration-dependent and most relevant to injection or topical use.
Inflammatory and hemolytic effects
- LL-37 has anti-inflammatory properties at physiological concentrations, but excessive levels can drive inflammation, as seen in rosacea.
- At very high concentrations (>50 μM), LL-37 can rupture (lyse) red blood cells; therapeutic concentrations (1-10 μM) stay well below this threshold.
Theoretical autoimmune concern
LL-37 forms complexes with the body's own DNA and RNA that can activate certain immune cells through the TLR9 and TLR7 receptors, which may trigger autoimmune responses. This mechanism is implicated in psoriasis but has not been observed as a side effect of external LL-37 at therapeutic doses.
Section 08
Regulatory Status
It is not on the 503A Bulks List either, so US compounding pharmacies have no lawful route to prepare it, and the furthest clinical data belongs to a synthetic derivative rather than the native peptide.
FDA compounding
No lawful route to compound it
LL-37 has no FDA-approved indication and was not on the 503A Bulks List as of 5 August 2026; section 503A lets a pharmacy compound from a bulk substance only when it carries a USP/NF monograph, is a component of an approved drug or appears on that list. The Pharmacy Compounding Advisory Committee is due to review it again before the end of February 2027.
Clinical development
Furthest trials use a synthetic analog
Ropocamptide, a synthetic LL-37 derivative developed by Promore Pharma, completed a phase IIb trial in venous leg ulcers with 28.1% complete wound closure versus 8.1% on placebo in the large-wound subgroup, and is being prepared for phase III. Native LL-37 remains earlier in development, with phase I/II trials completed for chronic wound care.
WADA
Not on the Prohibited List
LL-37 is not named on WADA's Prohibited List and is not treated as a controlled substance in any jurisdiction; its regulatory path runs through wound-care and anti-infective drug development rather than sport.
Absence from the 503A Bulks List is a legal fact about compounding, not an FDA judgement about safety or efficacy for any specific condition. Regulatory status differs between jurisdictions and can change — check the current position of your own regulator before relying on any of this.
Section 09
Research Studies
- [1]A comprehensive summary of LL-37, the factotum human cathelicidin peptideVandamme D, Landuyt B, Luyten W, Schoofs L · Cellular Immunology · 2012
- [2]Little Peptide, Big Effects: The Role of LL-37 in Inflammation and Autoimmune DiseaseKahlenberg JM, Kaplan MJ · The Journal of Immunology · 2013
- [3]Mechanism of Lipid Bilayer Disruption by the Human Antimicrobial Peptide, LL-37Henzler Wildman KA, Lee DK, Ramamoorthy A · Biochemistry · 2003
- [4]Physiologically-relevant modes of membrane interactions by the human antimicrobial peptide, LL-37, revealed by SFG experimentsDing B, Soblosky L, Nguyen K, et al. · Scientific Reports · 2013
- [5]Human host defense peptide LL-37 prevents bacterial biofilm formationOverhage J, Campisano A, Bains M, et al. · Infection and Immunity · 2008
- [6]LL-37, the neutrophil granule- and epithelial cell-derived cathelicidin, utilizes formyl peptide receptor-like 1 (FPRL1) as a receptor to chemoattract human peripheral blood neutrophils, monocytes, and T cellsYang D, Chen Q, Schmidt AP, et al. · The Journal of Experimental Medicine · 2000
- [7]Induction of Keratinocyte Migration via Transactivation of the Epidermal Growth Factor Receptor by the Antimicrobial Peptide LL-37Tokumaru S, Sayama K, Shirakata Y, et al. · The Journal of Immunology · 2005
- [8]An angiogenic role for the human peptide antibiotic LL-37/hCAP-18Koczulla R, von Degenfeld G, Kupatt C, et al. · Journal of Clinical Investigation · 2003
- [9]Antimicrobial and Chemoattractant Activity, Lipopolysaccharide Neutralization, Cytotoxicity, and Inhibition by Serum of Analogs of Human Cathelicidin LL-37Ciornei CD, Sigurdardottir T, Schmidtchen A, Bodelsson M · Antimicrobial Agents and Chemotherapy · 2005
Section 10
Frequently Asked Questions
LL-37 is the only cathelicidin-type antimicrobial peptide humans produce, released from immune and skin cells during infection or injury. It kills bacteria by punching into their membranes, disrupts biofilms at concentrations too low to kill bacteria outright, and separately signals immune cells and skin cells through the FPR2 receptor to help control inflammation and support wound repair — distinct, separately studied mechanisms rather than one single action.
Results are mixed. In venous leg ulcers, a placebo-controlled trial found the lowest two of three tested concentrations improved wound closure while the highest concentration was toxic to ulcer tissue. In diabetic foot ulcers, a 25-patient randomized trial moved a granulation-tissue score but showed no difference from placebo in wound area, inflammation markers, or bacterial counts.
Human safety data is limited to small phase 1/2 wound-healing trials using topical or local application — nothing supports whole-body injection. It is toxic to human cells at concentrations only 5 to 10 times above the antimicrobial range, can trigger mast-cell histamine release causing redness and itching, and at very high concentrations can rupture red blood cells; trial concentrations stayed below that threshold.
Every dose on record went onto a wound or directly into a tumor: 12.5 to 80 µg per cm² of ulcer twice weekly in leg-ulcer trials, or 250 to 500 µg injected straight into melanoma lesions in a four-patient study. The 100 to 250 µg daily subcutaneous dosing that circulates outside trials for whole-body use has never been tested in any published study.
The evidence pulls in different directions by cancer type. In gastric and colon cancer cell cultures LL-37 or an analogue slowed cell growth, but in ovarian cancer cell studies it did the opposite — it promoted rather than killed the cancer cells. All of this comes from cell-culture experiments, not animal tumor models or human trials, so neither a protective nor a harmful effect in a living person is established.
The opposite framing fits the evidence better — LL-37 is implicated as part of the disease process in both conditions rather than as a treatment. Its overexpression is thought to contribute to rosacea, and its tendency to form complexes with self-DNA and self-RNA that activate immune receptors is implicated in psoriasis pathogenesis, not proposed as a psoriasis therapy anywhere in the sourced material.
The lyophilized powder holds up for 12 to 18 months at −20°C or up to 3 months at 2–8°C. Once reconstituted in water it should be kept at 2–8°C, used within 14 days, and kept below 1 mg/mL, since LL-37 tends to clump into oligomers at higher concentrations.