LL-37
Endogenous cationic antimicrobial peptide (37 amino acids) derived from the C-terminal of hCAP-18
- Class
- Antimicrobial peptide
- Half-life
- ~1-2 hours
- Route
- Topical
- Cadence
- Multiple per week
- Evidence
- Mixed / early human
Overview
LL-37 is the only human cathelicidin — a natural antimicrobial peptide your immune cells already make and release at infection sites. It kills bacteria, fungi, and some viruses by physically punching holes in their membranes, not by targeting their metabolism the way antibiotics do. That membrane-disruption mechanism makes resistance almost impossible to develop. Beyond killing pathogens directly, it modulates your immune response — dampening excessive inflammation while recruiting the right immune cells to the right place.
The strongest human evidence is in wound healing. A Phase I/IIa randomised trial in 34 people with chronic venous leg ulcers that wouldn't close showed that topical LL-37 (0.5 mg/mL applied twice weekly for 4 weeks) increased the healing rate about sixfold vs placebo. Higher doses (3.2 mg/mL) showed no benefit — LL-37 is cytotoxic to your own cells at high concentrations, so more is not better. It's been tested topically for wounds, subcutaneously for sepsis models, and orally (via genetically modified bacteria) in a small COVID-19 trial, though that last one is exploratory and far from proven.
The catch: it's not FDA-approved for anything. The peptide you'll find in research markets is unregulated — purity, sterility, and actual LL-37 content vary widely between sellers. The safety profile in the wound-healing trials was good (adverse events around 8–12%, mostly mild injection-site redness), but almost all human data is topical. What happens with repeated subcutaneous dosing — especially at the doses people are experimenting with — is largely unknown.
Safety considerations
A few of the safety signals worth knowing — the full list, with dosing context and what to monitor, is inside AIx Core.
- Not approved by FDA, EMA, or any other regulator for any indication. Research-market peptides are unregulated — purity, sterility, and actual peptide content vary.
- Adverse event rate in Phase I/IIa wound trials was 8–12%, mostly mild injection-site erythema (redness) resolving within 24–48 hours. No serious adverse events, anaphylaxis, or systemic toxicity documented at therapeutic doses (topical 0.5–1.6 mg/mL).
- Cytotoxic to mammalian cells at high concentrations (>10 µM / 3 mg/mL). More is not better — dose escalation above the therapeutic window shown in trials is risky.
+ 4 more safety notes inside AIx Core →
Commonly monitored
Markers and signals people track when researching LL-37.
- Wound healing progress (if using topically) — measure wound area, granulation tissue formation
- Injection-site reactions — redness, swelling, pain lasting >48 hours
- Signs of excessive immune activation — fever, fatigue, unexplained inflammatory markers
- High-sensitivity CRP (hs-CRP) — tracks systemic inflammatory state; LL-37 can push it either direction
- Infection recurrence or resistance patterns if using chronically for antimicrobial support
- Skin changes — LL-37 levels are elevated in psoriasis, rosacea, and contact dermatitis; exogenous dosing could theoretically worsen these
Frequently asked questions
What is LL-37?
Endogenous cationic antimicrobial peptide (37 amino acids) derived from the C-terminal of hCAP-18. LL-37 is the only human cathelicidin — a natural antimicrobial peptide your immune cells already make and release at infection sites. It kills bacteria, fungi, and some viruses by physically punching holes in their membranes, not by targeting their metabolism the way antibiotics do. That membrane-disruption mechanism makes resistance almost impossible to develop. Beyond killing pathogens directly, it modulates your immune response — dampening excessive inflammation while recruiting the right immune cells to the right place.
How is LL-37 administered?
Topical, typically multiple per week.
What is the half-life of LL-37?
~1-2 hours — Short plasma half-life; local tissue effects persist longer at wound sites.
Is LL-37 approved for human use?
LL-37 is investigational — not approved by the FDA, EMA, or MHRA for human use at the time of writing.
What does the evidence show for LL-37?
Evidence tier: Mixed / early human. Grönberg et al. 2014 (Phase I/IIa, n=34, chronic venous leg ulcers): topical LL-37 at 0.5 mg/mL applied twice weekly for 4 weeks increased healing rate constant ~6-fold vs placebo (p=0.003). The 1.6 mg/mL dose was ~3-fold better; the 3.2 mg/mL dose showed no benefit.
What is commonly monitored when researching LL-37?
Commonly tracked markers + signals: Wound healing progress (if using topically) — measure wound area, granulation tissue formation, Injection-site reactions — redness, swelling, pain lasting >48 hours, Signs of excessive immune activation — fever, fatigue, unexplained inflammatory markers, High-sensitivity CRP (hs-CRP) — tracks systemic inflammatory state; LL-37 can push it either direction, Infection recurrence or resistance patterns if using chronically for antimicrobial support, Skin changes — LL-37 levels are elevated in psoriasis, rosacea, and contact dermatitis; exogenous dosing could theoretically worsen these.
Related compounds
Open this in AIx Core for the full picture
Mechanism breakdown, receptor pathway diagram, full safety list, monitored items, source citations, and one-tap add-to-protocol. Free with any account.