LL-37
Immune, Antimicrobial
In short
- The only human cathelicidin antimicrobial peptide — a genuine component of innate immunity, not a synthetic construct.
- Broad antimicrobial activity plus immunomodulatory and wound-healing roles.
- Has genuinely reached human clinical trials, including a phase 2 in venous leg ulcers.
- Its biology is double-edged: LL-37 is implicated in the pathology of rosacea and psoriasis, where excess is the problem.
- Not approved. Concentration-dependent cytotoxicity is a real consideration.
Structure
How it works
LL-37 is a 37-amino-acid cationic peptide cleaved from hCAP18, expressed by neutrophils and epithelial cells. Its positive charge and amphipathic structure let it disrupt bacterial membranes directly, giving broad activity against gram-positive and gram-negative bacteria, some fungi, and enveloped viruses.
Beyond direct killing it acts as an immune signal: chemoattracting neutrophils, monocytes, and T cells, neutralising LPS, and promoting angiogenesis and re-epithelialisation in wounds.
Because its mechanism is membrane disruption, selectivity between microbial and host membranes is concentration-dependent — which is the origin of its cytotoxicity at higher concentrations.
What the research shows
A phase 1/2 trial of topical LL-37 in hard-to-heal venous leg ulcers reported improved healing rates at lower doses, with the notable finding that the highest dose performed worse — consistent with concentration-dependent cytotoxicity.
Preclinical work supports antimicrobial and wound-healing activity broadly.
Elevated LL-37 is implicated in the pathogenesis of rosacea, and it acts as an autoantigen in psoriasis — so more is not better, and in some tissues more is actively harmful.
Dosing in the literature
Figures below are quoted from published studies, with the species or population they were measured in. They are records of what was studied, not recommendations.
| Studied in | Amount | Route | Source |
|---|---|---|---|
| Human — phase 1/2 topical trial in venous leg ulcers | Topical 0.5 and 1.6 mg/mL improved healing; 3.2 mg/mL did not | topical | PubMed |
Commonly reported ranges
These are amounts people report using. They are not from any study, have not been evaluated for safety, and are reproduced here only because they circulate widely and are better seen alongside the evidence than instead of it.
| Reported by | Amount | Route |
|---|---|---|
| Commonly reported | 100–500 µg daily, in short courses | subcutaneous |
No published human pharmacokinetic study establishes a dose, interval, or duration for this compound. Community figures below have no trial behind them and are reports of practice, not evidence. The dose-response in the human trial was non-monotonic — the highest concentration performed worse than lower ones. For a membrane-disrupting peptide, more is not simply more, and this is one of the few compounds here where that is demonstrated rather than theoretical.
Handling and storage
Supplied as a lyophilised powder requiring reconstitution with bacteriostatic water. The powder is comparatively stable; once reconstituted it is refrigerated and used within weeks. Track the date you reconstitute each vial — the Inventory section does this, and it is the difference between knowing a vial is three weeks old and guessing.
The human evidence is topical. Subcutaneous injection is the community route and has no supporting trial data.
Side effects
The topical trial reported acceptable tolerability at effective doses.
The main concern is concentration-dependent cytotoxicity to host cells, which follows directly from the membrane-disruption mechanism and was visible in the trial's dose-response.
Given its role as an autoantigen in psoriasis and its involvement in rosacea, systemic administration in anyone with those conditions carries a specific theoretical risk of worsening them.
Combinations
No interaction data exists. Combining an antimicrobial peptide with conventional antibiotics has been explored preclinically for synergy but not established clinically.
Research status
A substantial and legitimate literature spanning innate immunity, antimicrobial resistance, and wound healing. This is real immunology, not a research-chemical curiosity.
Therapeutic development has been limited by cytotoxicity and by the cost and stability of peptide manufacture.
Legal status
Not approved for any indication in any jurisdiction. Sold for research use only.
WADA status
Not specifically named on the Prohibited List. Falls under WADA class S0, which prohibits any pharmacological substance not currently approved by any governmental regulatory health authority for human therapeutic use. Treat it as prohibited in sport.
Conclusion
LL-37 is a real and important piece of human immunology with a genuine clinical trial behind it — and that trial found the highest dose worked worst.
It is also a peptide your body already regulates carefully, and the conditions where it is elevated (rosacea, psoriasis) are ones where the excess causes the disease. That asymmetry deserves more attention than it usually gets.
Sources
Track your own LL-37 protocol
Peppers logs your doses, models your levels from this half-life, tracks your vials and tells you when you will run out. Free on iPhone.
Reference and educational information only. Not medical advice. Nothing here diagnoses, treats, or prescribes, and nothing here is a recommendation to use any compound. The compounds described are research chemicals and are not approved for human consumption. Legal and anti-doping status change — the review date above is when these claims were last checked. Talk to a qualified clinician about anything you intend to take.