LL-37
Human cathelicidin-derived antimicrobial peptide (37 amino acids) that disrupts bacterial membranes at MIC 0.62 μM against S.
aureus, neutralizes endotoxin (LPS) to prevent septic shock, and has reached Phase II clinical trials as Ropocamptide for wound healing — achieving 6-fold accelerated healing at 0.5 mg/mL in venous leg ulcers
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Suggested dose
0.5 – 1.6 mg
Compound profile
Scientific & efficacy data
Immune
Peptide profile
Moderate human trials
LL-37
0.5 mg/mL gel · Once daily
Molecular formula
C205H340N60O53
- Mol. weight
- 4,493.26 Da
- CAS number
- 154947-66-7
- PubChem
- 16198951
- Developed · 1995-1996 (initial identification and characterization); 2014 (Phase I/IIa clinical trial); clinical development ongoing
- Endogenous; developed by Prokera Biologics
Prokera Biologics / OncolyticsBiotech
Amino acid sequence
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTESWound Healing
Clinical trials show this peptide heals stubborn wounds six times faster than placebo by boosting new blood vessel growth and tissue repair.
Fighting Infections
Works like a natural antibiotic in your body, punching holes in harmful bacteria including drug-resistant strains that normal antibiotics can't kill.
Immune Boost
Calls your immune cells to action like a chemical alarm, helping your body mount a stronger defense against bacteria, fungi, and viruses.
Dosing
How much do I take?
0.5 – 1.6 mg · twice weekly
0.5 – 1.6 mg
Twice weekly
Covers all 2 documented dose levels · timing · dose-adjustment guidance.
Suitability
Is this right for me?
Best for treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers & immune defense against antibiotic-resistant bacterial infections (mrsa, pseudomonas)
Best for
Treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers
LL-37 is particularly well-suited for individuals focused on treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Immune defense against antibiotic-resistant bacterial infections (MRSA, Pseudomonas)
LL-37 is particularly well-suited for individuals focused on immune defense against antibiotic-resistant bacterial infections (mrsa, pseudomonas). Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Anti-biofilm strategies for chronic wound infections and medical device-associated infections
LL-37 is particularly well-suited for individuals focused on anti-biofilm strategies for chronic wound infections and medical device-associated infections. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Boosting innate immune defense in immunocompromised or aging individuals
LL-37 is particularly well-suited for individuals focused on boosting innate immune defense in immunocompromised or aging individuals. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Consider alternatives if
Do not use if
Use with caution if
Not sure?
Compare LL-37 with similar peptides to find the best fit for your goals.
Administration
How do I use it?
Topical application (wound healing) · Subcutaneous injection (research)
Route
LL-37 is administered Topical application (wound healing)—no injection required
Best sites
Covers reconstitution · step-by-step technique · storage · a sample daily schedule.
Safety
Is it safe?
4 common side effects · 2 serious
LL-37 is an endogenous cathelicidin antimicrobial peptide naturally produced by immune cells and epithelial tissues, conferring inherent biocompatibility and low toxicity at physiological concentrations.
Synthetic LL-37 shows excellent safety in in vitro immune assays and animal models with no hepatotoxicity, nephrotoxicity, or genotoxicity at relevant doses.
At elevated concentrations, the cationic amphipathic structure can cause hemolysis and cell membrane damage, but therapeutic doses are far below these thresholds. Injection site reactions are minimal in research applications.
LL-37 safety derives from extensive basic research in immunology and dermatology journals (Nature Immunology, Journal of Immunology) demonstrating antimicrobial activity, wound healing promotion, and immune modulation without systemic toxicity.
Human clinical data are limited—most applications remain in vitro or preclinical. Phase 1 safety and pharmacokinetics data suggest good tolerability, but Phase 2+ efficacy trials in infectious disease and skin conditions are ongoing.
The peptide is generally recognized as safe for topical and research applications.
Common side effects · experienced by some users
Local site irritation
Mild redness, warmth, or irritation at the wound application site. This is the most frequently reported adverse effect in clinical trials and reflects the peptide's interaction with wound-bed tissues.
Management: Generally self-limiting. If irritation is significant, reduce application frequency to every other day. Ensure wound is gently cleansed before application.
Transient stinging or burning
Brief stinging or burning sensation upon application to open wound surfaces, typically lasting seconds to minutes.
Management: Allow reconstituted solution to reach room temperature before application. Sensation typically diminishes with subsequent applications as wound healing progresses.
Mild perilesional erythema
Redness in the skin surrounding the treated wound area, reflecting local immune activation and increased blood flow from LL-37-induced angiogenesis.
Management: Usually indicates active healing response. Monitor for signs of infection versus expected inflammatory healing. Should remain localized and non-spreading.
Increased wound exudate
Temporary increase in wound fluid production during initial treatment phase as antimicrobial and pro-healing mechanisms activate.
Management: Use appropriate absorbent wound dressings. Typically normalizes within 1-2 weeks as healing progresses and bacterial bioburden is reduced.
Less common
These typically resolve with continued use or dose adjustment.
Stop and seek help if
- Severe or worsening side effects that don't improve with dose adjustment or supportive care
- Signs of an allergic reaction—rash, hives, swelling, or difficulty breathing
- Your healthcare provider recommends discontinuation based on your clinical response
- Development of any new medical condition that may be contraindicated with LL-37
- Pregnancy or planning to become pregnant (unless specifically approved for use during pregnancy)
- Abnormal lab results or clinical markers that suggest adverse effects
LL-37 should only be started, adjusted, or discontinued under medical supervision. This information is for educational purposes only and does not replace professional medical advice. Never stop a prescribed treatment without consulting your healthcare provider first, as abrupt discontinuation may have consequences.
With other peptides
- Safe:Conventional wound dressings (hydrogels, alginates) — LL-37 can be incorporated into wound matrices for sustained delivery and enhanced antimicrobial protection — May be used together under medical guidance.
- Safe:Silver-based antimicrobials — synergistic bactericidal activity through complementary membrane disruption mechanisms — May be used together under medical guidance.
- Safe:Growth factors (PDGF, EGF) — LL-37 promotes angiogenesis while growth factors drive tissue regeneration for comprehensive wound healing — May be used together under medical guidance.
With medications
- Caution:High-concentration saline solutions — elevated salt concentrations can reduce LL-37 antimicrobial activity through charge shielding effects — Use with caution—discuss with your healthcare provider.
- Caution:Anionic surfactants or dressings — may bind and inactivate the cationic LL-37 peptide through electrostatic complexation — Use with caution—discuss with your healthcare provider.
- Caution:Serum-rich wound environments without dose adjustment — serum proteins can partially sequester LL-37 and reduce effective concentration — Use with caution—discuss with your healthcare provider.
With supplements
- Safe:Multivitamins — Generally safe to take alongside LL-37. Space doses apart if taking oral formulations to ensure optimal absorption.
- Safe:Electrolyte supplements — Helpful if experiencing any GI side effects that could lead to dehydration. Safe to combine.
Effectiveness
How do I know it's working?
Moderate human trials · first signs days 1-7
Evidence level
Moderate human trials
(Phase 1-2)
Regulatory status
Research compound
Onset of effects
Moderate
(1-2 weeks)
How it works
LL-37 is the active form of cathelicidin, an antimicrobial peptide your immune cells produce to kill bacteria, viruses, and fungi while also reducing inflammation and promoting wound healing.
The deeper mechanism
LL-37 (also known as hCAP-18 C-terminal 37 amino acids) is a 37-amino acid cationic α-helical peptide derived from proteolytic processing of the hCAP18 precursor by neutrophil elastase and cathepsin G.
LL-37 exhibits potent antimicrobial activity through multiple mechanisms: direct membrane disruption via formation of membrane-spanning pores, sequestration of lipopolysaccharides and lipoteichoic acids, intracellular targeting of bacterial nucleic acids, and autophagy induction.
Beyond antimicrobial functions, LL-37 modulates innate and adaptive immunity through TLR9 signaling, promotes chemotaxis of immune cells via formyl peptide receptor-like 1 (FPRL-1/LIPOXIN A4 receptor) activation, enhances angiogenesis and wound healing, and suppresses excessive inflammatory responses through IL-10 upregulation.
What to expect
Days 1-7
What you might notice
- Reduction in wound bioburden and bacterial colonization from direct antimicrobial activity
- Initial wound bed preparation with cleaner, healthier-appearing granulation tissue
- Possible mild local irritation or stinging upon application that improves with repeated use
- Early recruitment of immune cells to wound site through FPRL1-mediated chemotaxis
What's normal
- The antimicrobial effect begins immediately upon contact with wound bed
- Increased wound exudate is common during the first week as bacterial killing and immune activation occur
- Visible wound changes may be subtle initially — the peptide is establishing conditions for healing
What's next
- Continue daily application as tolerated
- Expect wound bed to transition from inflammatory to proliferative phase
- Take baseline wound measurements and photographs for tracking progress
Week 2-4
What you might notice
- Visible wound size reduction and epithelial advancement from wound edges
- Improved granulation tissue quality with increased vascularity (LL-37-induced angiogenesis)
- Reduced wound odor and signs of bacterial infection
- In the Phase I/IIa trial, the 0.5 mg/mL group showed 6-fold accelerated healing at this timepoint
What's normal
- Progressive wound contraction and re-epithelialization are expected
- Some wounds heal faster than others depending on underlying conditions (venous insufficiency, diabetes)
- Periwound erythema should be stable or decreasing — increasing redness may indicate infection
What's next
- Continue treatment until wound closure or per clinical protocol (typically 4-12 weeks)
- Document weekly wound measurements to track healing trajectory
- Assess whether to continue current concentration or adjust based on response
Week 4-12
What you might notice
- Continued wound closure with re-epithelialization and scar maturation
- Significant reduction or complete elimination of chronic wound biofilm
- Wound may reach complete closure during this period for many patients
- Stable, healthy wound bed without signs of recurrent infection
What's normal
- Healing rates vary — some chronic wounds may require the full 12-week course
- The anti-biofilm effects help prevent the recurrent infections common in chronic wounds
- Newly healed tissue may appear pink or slightly different from surrounding skin
What's next
- Upon wound closure, discontinue LL-37 application
- Maintain standard wound care and compression therapy if applicable
- Monitor for wound recurrence at follow-up visits
Signs it's working
Treatment Response
- Improvement in the primary symptoms or condition being treated
- Positive changes in relevant lab values or clinical markers
- Consistent, stable response to LL-37 over time
- Reduction in symptom frequency or severity
General Well-being
- Improved energy levels and daily functioning
- Better quality of life related to the treated condition
- Manageable or absent side effects indicating good tolerance
- Positive feedback from healthcare provider during check-ups
Not seeing results? Common reasons
- Not at therapeutic dose yet—initial doses are for building tolerance, not maximum effect
- Insufficient time at target dose—most compounds need several weeks to show full benefits
- Inconsistent dosing schedule—regular, consistent use is crucial for optimal results
- Individual variation in response—genetics, metabolism, and other factors affect outcomes
- Underlying conditions or medications interfering with absorption or effectiveness
- Improper storage leading to degraded product—always verify proper storage conditions
Key research
Questions
Frequently asked
What is LL-37 and what does the name mean?
LL-37 is the only cathelicidin antimicrobial peptide found in humans. The name derives from its first two amino acids (both Leucine, abbreviated 'L') and its total length of 37 amino acids. It is cleaved from the C-terminus of the 18 kDa precursor protein hCAP-18 (human cationic antimicrobial protein) by proteinase 3 in neutrophils and by kallikreins in skin. Stored in neutrophil specific granules and secreted by epithelial cells, LL-37 is a first-line innate immune defense peptide expressed by the CAMP gene on chromosome 3.
How did LL-37 perform in clinical trials for wound healing?
LL-37 (under the pharmaceutical name Ropocamptide, developed by Promore Pharma in Sweden) completed a Phase I/IIa clinical trial with 34 patients with hard-to-heal venous leg ulcers. The 0.5 mg/mL topical formulation demonstrated a 6-fold greater healing rate compared to placebo over 4 weeks. A larger 148-patient Phase IIb trial has also been completed. The wound healing mechanism involves LL-37's combined antimicrobial, anti-biofilm, angiogenic, and keratinocyte migration-promoting activities.
Why is LL-37 important for fighting antibiotic-resistant bacteria?
Unlike conventional antibiotics that target specific molecular pathways (which bacteria can evolve resistance to), LL-37 kills bacteria through physical membrane disruption — its cationic charge attracts it to anionic bacterial membranes, and its alpha-helical structure creates pores that rapidly lyse the cell. This physical mechanism makes resistance development much more difficult. Additionally, LL-37 disrupts bacterial biofilms, which are the primary reason chronic wound infections resist antibiotic treatment, and it recruits immune cells to clear remaining bacteria.
What is the connection between vitamin D and LL-37?
Vitamin D directly induces the expression of the CAMP gene that encodes hCAP-18 (the LL-37 precursor protein). The vitamin D receptor (VDR) binds to a vitamin D response element in the CAMP promoter, upregulating LL-37 production. This molecular mechanism is a key reason vitamin D supplementation supports immune function — it boosts the body's production of its primary antimicrobial peptide. Vitamin D deficiency is associated with reduced LL-37 levels and increased infection susceptibility.
Why can't LL-37 be used as a systemic antibiotic via IV injection?
LL-37 demonstrates concentration-dependent hemolytic activity — at higher systemic concentrations needed for parenteral antimicrobial therapy, the peptide's membrane-disrupting mechanism also affects human red blood cells. Additionally, serum proteins partially bind and inactivate the peptide, and its half-life in circulation is short due to rapid proteolytic degradation. This is why clinical development has focused on topical wound application, where high local concentrations can be achieved without systemic hemolysis concerns.
How does LL-37 differ from conventional antibiotics in treating wound infections?
LL-37 provides a fundamentally different approach: rather than targeting a single bacterial pathway, it physically disrupts membranes, neutralizes endotoxin, destroys biofilms, recruits immune cells, and simultaneously promotes wound healing through angiogenesis and keratinocyte migration. Conventional antibiotics kill bacteria but do not promote healing, cannot penetrate biofilms effectively, and face resistance evolution. LL-37 addresses all these limitations while remaining effective against antibiotic-resistant strains including MRSA and multi-drug resistant Pseudomonas.
Further reading
History & related research
History · since 1995
Your Body's Built-In Antibiotic That Superbugs Can't Outsmart
When the world's strongest antibiotics started failing against deadly superbugs, scientists found an ancient weapon hiding inside your own immune cells — a tiny peptide that has been fighting bacteria for millions of years without ever losing its edge.
Read the full history of LL-37Ready for the protocol?
Every dosing tier, administration route, timing note, and dose-adjustment rule for LL-37, on one page.