Is LL-37 approved as a drug?

No. Synthetic LL-37 is not approved as a medicinal product by the FDA, EMA, MHRA, or any major regulator. Clinical trials have evaluated topical LL-37 in wound healing (Phase 1/2a and Phase 2b), but these have not led to regulatory approval. All synthetic LL-37 sold commercially is for research use only.

What is the evidence for LL-37 in wound healing?

There are three completed RCTs: a Phase 1/2a trial (n=34 venous leg ulcers, 2014) showing a 6-fold improvement in healing rate at 0.5 mg/mL; a Phase 2b trial (n=148 venous leg ulcers, 2021) where the primary endpoint was not reached in the full cohort but a significant benefit was seen in the large-ulcer subgroup; and a smaller RCT (n=25 diabetic foot ulcers, 2023) showing improved granulation tissue. All studies used topical application, not injection.

Does injecting LL-37 have any human evidence?

No controlled human evidence exists for injectable systemic LL-37. The clinical trials are exclusively topical wound-healing studies. Community injectable use is entirely anecdotal and represents extrapolation from in-vitro and animal mechanistic work.

What is LL-37's half-life?

Short and context-dependent. In animal models, plasma levels peak at 15–20 minutes and fall substantially by ~105 minutes. In wound environments or biological fluids, LL-37 is degraded rapidly by host and bacterial proteases. Human pharmacokinetic data for injected synthetic LL-37 have not been published.

What is the connection between LL-37 and skin diseases like rosacea and psoriasis?

LL-37 plays a pathological role in both conditions, though via different mechanisms. In rosacea, aberrant proteolytic processing by kallikreins generates proinflammatory peptide fragments that activate inflammasomes and drive vascular dilation and skin inflammation. In psoriasis, overexpressed LL-37 forms complexes with self-DNA that activate plasmacytoid dendritic cells, amplifying the autoimmune response. These are endogenous dysregulation phenomena, distinct from therapeutic exogenous LL-37 use.

Recovery

LL-37

Also known as: Cathelicidin, hCAP-18 C-terminal peptide, CAP-18, Human cathelicidin antimicrobial peptide

The only human cathelicidin — a 37-amino-acid host defence peptide cleaved from hCAP-18 — with direct antimicrobial, immunomodulatory, and wound-healing activities studied...

Last updated July 11, 2026

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Overview

LL-37 is a 37-amino-acid cationic amphipathic peptide representing the C-terminal cleavage product of hCAP-18 (human cationic antimicrobial protein 18 kDa), encoded by the CAMP gene. It is the only cathelicidin produced in humans and functions as a key effector of innate immune defence at epithelial surfaces. LL-37 is produced by neutrophils, macrophages, mast cells, natural killer cells, keratinocytes, and epithelial cells of the respiratory, gastrointestinal, and genitourinary tracts. LL-37 has three broad functional domains that make it a subject of ongoing research: direct broad-spectrum antimicrobial activity (membrane disruption against bacteria, fungi, enveloped viruses, and some parasites), immunomodulation (chemokine and cytokine induction, immune cell recruitment, modulation of toll-like receptor signalling), and tissue repair (promotion of wound healing, angiogenesis, and re-epithelialisation). Clinical interest in synthetic LL-37 as a therapeutic agent has grown from these observations. Small but genuine randomised controlled trials have evaluated topical LL-37 cream for chronic venous leg ulcers and diabetic foot ulcers, with encouraging wound-healing signals in early-phase work, though a larger Phase 2b trial in venous leg ulcers did not reach primary endpoint significance in the full cohort. Endogenous LL-37 dysregulation is also implicated in inflammatory skin diseases: overexpression in psoriasis and abnormal processing in rosacea contribute to their pathophysiology. Synthetic LL-37 is available from research suppliers. Its use outside approved clinical trials or medical supervision is for research purposes only, and it is not an approved drug in any jurisdiction.

How it works

LL-37's antimicrobial activity arises from its amphipathic alpha-helical structure in membrane environments: the peptide inserts into and disrupts bacterial, fungal, and viral lipid membranes through a carpet or toroidal-pore mechanism, causing membrane depolarisation and cell death. This activity is broad-spectrum but concentration-dependent; LL-37 is less cytotoxic to eukaryotic cells at physiological concentrations due to differences in membrane composition (phosphatidylcholine predominance vs. phosphatidylethanolamine and anionic lipids in bacteria). At higher concentrations, LL-37 can be cytotoxic to mammalian cells, which is a limitation for systemic use. Immunologically, LL-37 activates multiple host receptors including FPRL1 (formyl peptide receptor-like 1), TLR3, TLR4, and EGFR on epithelial and immune cells, modulating chemokine secretion (CXCL8, MCP-1), recruiting neutrophils and monocytes, and promoting dendritic cell maturation. It also suppresses excessive inflammation under some conditions, inhibiting LPS-induced TLR4 signalling by binding and sequestering LPS. In wound healing, LL-37 promotes keratinocyte migration through EGFR transactivation, focal adhesion kinase signalling, and matrix metalloproteinase activation, and supports angiogenesis, contributing to re-epithelialisation and granulation tissue formation. These mechanisms are well characterised in vitro and in animal models. In clinical skin diseases, aberrant LL-37 processing (kallikrein-mediated) generates proinflammatory fragments in rosacea, while overexpressed full-length LL-37 in psoriasis activates plasmacytoid dendritic cells by complexing with self-DNA, amplifying the autoimmune loop.

Researched effects

Clinical Topical LL-37 cream accelerated healing of hard-to-heal venous leg ulcers at lower doses in a Phase 1/2a RCT (n=34, 6-fold healing rate improvement at 0.5 mg/mL vs placebo)
Clinical Topical LL-37 cream enhanced granulation tissue formation in diabetic foot ulcers with mild infection in an RCT (n=25)
Preclinical Broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria, biofilms, fungi, and enveloped viruses in vitro
Preclinical Anti-biofilm activity against polymicrobial wound infections including MRSA and Pseudomonas aeruginosa in vitro and animal models
Preclinical Promotes keratinocyte migration, re-epithelialisation, and angiogenesis in wound healing models
Preclinical Immunomodulatory: chemokine-mediated immune cell recruitment and LPS-sequestration in in vitro models
Anecdotal Community-reported subcutaneous use for general immune support and antimicrobial properties

Evidence levels: Clinical (human trials) · Preclinical (animal/lab) · Anecdotal (community-reported).

Dosing reference

For research reference only — not a recommendation.

Clinical / studied dosing

Phase 1/2a venous leg ulcer trial (Grönberg et al., Wound Repair and Regeneration, 2014; n=34): topical LL-37 at 0.5, 1.6, or 3.2 mg/mL applied twice weekly for 4 weeks — 0.5 and 1.6 mg/mL produced the best outcomes; 3.2 mg/mL showed no benefit over placebo. Phase 2b venous leg ulcer trial (Mahlapuu et al., 2021; n=148): 0.5 or 1.6 mg/mL topically with compression; primary endpoint (complete healing) not reached in full cohort; significant benefit in large-ulcer subgroup. Diabetic foot ulcer RCT (Miranda et al., Arch Dermatol Res, 2023; n=25): 0.5 mg/g cream applied at 0.025 mL/cm², twice weekly for 4 weeks. No systemic (injectable) dosing has been established in human trials.

Community-reported dosing (anecdotal)

Anecdotal and research-reference only; not medical advice. Community and vendor sources (peptide forums, research vendor guides) describe subcutaneous injection protocols of typically 100–500 mcg per dose once daily, sometimes twice daily, in cycles of 4–8 weeks, based on extrapolation from the antimicrobial and immune-modulating preclinical literature. There are no human PK or efficacy data supporting injectable use of LL-37 in these contexts. Topical application of research-grade LL-37 to wounds is also described, mirroring the clinical trial approach. All such uses are entirely experimental and outside controlled evaluation.

Half-life: Short and context-dependent. In murine models, radiolabelled LL-37 shows peak plasma concentration within 15–20 minutes of injection, with approximately 50% clearance by ~105 minutes. In biological fluids and wound environments, LL-37 is rapidly degraded by host serine proteases (kallikreins, elastase), bacterial proteases (Staphylococcus aureus V8 protease, aureolysin), and peptide bond hydrolysis, substantially shortening its effective half-life at sites of infection or inflammation. Human pharmacokinetic data for synthetic LL-37 after parenteral administration have not been published.
Routes: topical, subcutaneous

Safety & side effects

Topical LL-37 in clinical trials has been well tolerated at concentrations up to 1.6 mg/mL applied twice weekly. Local application at 3.2 mg/mL showed no efficacy advantage and was not associated with systemic toxicity in the published wound trials. No serious adverse events attributable to LL-37 were reported in the published clinical trials. A key concern for any systemic (injectable) use is concentration-dependent cytotoxicity: LL-37 disrupts mammalian cell membranes at sufficiently high concentrations, which has limited its development as an injectable systemic antimicrobial. In inflammatory skin disease research, LL-37 overexpression or abnormal processing is associated with pathological inflammation (rosacea, psoriasis), demonstrating that the peptide can drive inflammatory cascades when dysregulated. Research-grade synthetic LL-37 for injection is not produced under pharmaceutical manufacturing standards; purity, sterility, and concentration are not independently verified. LL-37 is not approved as a drug by the FDA, EMA, MHRA, or any major regulator. Its use outside controlled clinical trials is not endorsed and is for research purposes only.

Research summary

LL-37's biology as the sole human cathelicidin is thoroughly characterised in peer-reviewed literature spanning two decades. Its antimicrobial, immunomodulatory, and wound-healing properties are robustly established in vitro and in animal models, and the endogenous roles of LL-37 dysregulation in rosacea, psoriasis, and chronic wound pathophysiology have been confirmed in human disease studies. The translational clinical picture is small but real. Two completed RCTs of topical LL-37 in chronic venous leg ulcers provide the most direct human evidence: the Phase 1/2a study (n=34) showed striking healing rate improvements at lower doses (6-fold at 0.5 mg/mL), and a subsequent Phase 2b trial (n=148) demonstrated a statistically significant benefit in the large-ulcer subgroup, though the primary endpoint in the full cohort was not reached — a common pattern in wound healing trials with heterogeneous populations. A smaller RCT in diabetic foot ulcers (n=25, 2023) showed enhanced granulation tissue formation. Together these trials provide limited but genuine clinical evidence for topical application in wound healing, while confirming the safety of topical administration. For injectable systemic use, which is the primary form in the research-peptide community, essentially no human evidence exists. The cytotoxicity-at-high-concentration limitation has been a significant barrier to systemic development. Whether systemic subcutaneous dosing at the lower concentrations described anecdotally produces clinically meaningful antimicrobial or immunomodulatory effects in humans is unknown. The honest summary: LL-37 is a well-characterised innate immune effector with genuine preclinical mechanistic depth and limited but real wound-healing clinical evidence from small trials. Its systemic (injectable) use as a research compound is extrapolation well beyond the current evidence base.

FAQ

Is LL-37 approved as a drug?: No. Synthetic LL-37 is not approved as a medicinal product by the FDA, EMA, MHRA, or any major regulator. Clinical trials have evaluated topical LL-37 in wound healing (Phase 1/2a and Phase 2b), but these have not led to regulatory approval. All synthetic LL-37 sold commercially is for research use only.
What is the evidence for LL-37 in wound healing?: There are three completed RCTs: a Phase 1/2a trial (n=34 venous leg ulcers, 2014) showing a 6-fold improvement in healing rate at 0.5 mg/mL; a Phase 2b trial (n=148 venous leg ulcers, 2021) where the primary endpoint was not reached in the full cohort but a significant benefit was seen in the large-ulcer subgroup; and a smaller RCT (n=25 diabetic foot ulcers, 2023) showing improved granulation tissue. All studies used topical application, not injection.
Does injecting LL-37 have any human evidence?: No controlled human evidence exists for injectable systemic LL-37. The clinical trials are exclusively topical wound-healing studies. Community injectable use is entirely anecdotal and represents extrapolation from in-vitro and animal mechanistic work.
What is LL-37's half-life?: Short and context-dependent. In animal models, plasma levels peak at 15–20 minutes and fall substantially by ~105 minutes. In wound environments or biological fluids, LL-37 is degraded rapidly by host and bacterial proteases. Human pharmacokinetic data for injected synthetic LL-37 have not been published.
What is the connection between LL-37 and skin diseases like rosacea and psoriasis?: LL-37 plays a pathological role in both conditions, though via different mechanisms. In rosacea, aberrant proteolytic processing by kallikreins generates proinflammatory peptide fragments that activate inflammasomes and drive vascular dilation and skin inflammation. In psoriasis, overexpressed LL-37 forms complexes with self-DNA that activate plasmacytoid dendritic cells, amplifying the autoimmune response. These are endogenous dysregulation phenomena, distinct from therapeutic exogenous LL-37 use.
Is LL-37 safe to use?: Topical LL-37 at therapeutic wound-healing concentrations has been well tolerated in clinical trials with no serious adverse events. A safety concern for systemic use is its concentration-dependent cytotoxicity — LL-37 disrupts mammalian cell membranes at high concentrations. Injectable systemic safety has not been evaluated in humans. Research-grade LL-37 from unregulated suppliers carries additional risks of impurity and contamination.

References

All content is for research and educational use only and is not medical advice. Products are sold for laboratory research only and are not for human consumption.