LL-37
A natural human antimicrobial peptide and part of the innate immune system, studied for fighting microbes and supporting wound healing. It is a real and important molecule in the body, but its use as an injectable peptide is research-stage with little human trial data.
Quick take
- What it is: a natural human antimicrobial peptide (a cathelicidin) that is part of the body's first-line innate immune defence.
- What people use it for: fighting bacteria and other microbes and supporting wound healing.
- What we actually know: its biology is well studied, but using it as an administered peptide therapy is still research-stage with minimal human data.
- Status: not FDA-approved as a drug; sold only as an unapproved research peptide.
What it is
LL-37 is a natural human antimicrobial peptide. It is the active 37–amino-acid fragment released from a larger protein called cathelicidin (hCAP18), and it forms part of the body’s innate immune system — the fast, general first line of defence against microbes.1 It is found in skin, airway surfaces, and immune cells such as neutrophils.
Unlike many peptides on this site, LL-37 is not a lab invention but a molecule the body makes itself. The question that matters is whether administering extra LL-37 as a therapy is useful and safe — and here the evidence is far thinner than the rich biology might suggest.
How it works
LL-37 has several roles. It can directly disrupt the membranes of bacteria and other microbes, acting as a built-in antibiotic. It also acts as a signalling molecule that influences immune cells, can support wound healing and blood-vessel formation, and helps shape inflammatory responses.2
Importantly, these effects are double-edged: while LL-37 helps fight infection, it can also be pro-inflammatory, and dysregulated LL-37 has been linked to inflammatory and autoimmune conditions. That complexity makes it harder to turn into a simple therapy.
What the evidence shows
Laboratory and animal studies
The basic science is substantial. Laboratory and animal studies clearly demonstrate LL-37’s antimicrobial activity, its roles in wound healing, and its involvement in immune signalling.2,3 Researchers have explored LL-37 and synthetic analogues for infections and chronic wounds.
Human studies
In contrast, evidence for using administered LL-37 as a treatment in people is very limited. There are no established, well-validated human clinical uses of injected LL-37 of the kind marketed online. The honest summary is important natural biology, but minimal clinical evidence for its use as an external therapy.
Dosages reported in the literature
Informational only. The figures below describe the research context rather than any validated protocol. They are not a recommendation or a prescription. Appropriate use, if any, should be determined by a qualified healthcare professional.
| Setting | Route | Reported range |
|---|---|---|
| Laboratory / animal research | Varies | Experimental only; not applicable to humans |
| Anecdotal use | Subcutaneous | Reported in microgram amounts; not standardised or validated |
There are no dose-finding human trials for administered LL-37, so no range here should be read as established as safe or effective.
Safety & side effects
There are no long-term controlled human safety data for administered LL-37. Because the peptide can be pro-inflammatory and is implicated in some inflammatory and autoimmune processes, its safety profile when given as a therapy is genuinely uncertain and potentially complex.
As with all unregulated peptides, products sold as “LL-37” also raise concerns about identity, purity and dose accuracy — reinforcing the importance of professional oversight.
Legal & regulatory status
LL-37 is not approved by the FDA as a medicine, and it is not an approved drug elsewhere. It is sold only as an unapproved research peptide.4 Its status as a natural human molecule does not make administering it as a therapy approved or validated. Rules differ by country and change over time.
References
- Dürr UHN, Sudheendra US, Ramamoorthy A. LL-37, the only human member of the cathelicidin family of antimicrobial peptides. Biochim Biophys Acta. 2006;1758(9):1408-1425. [PMID 16716248, doi:10.1016/j.bbamem.2006.03.030]
- Vandamme D, Landuyt B, Luyten W, Schoofs L. A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cell Immunol. 2012;280(1):22-35. [PMID 23246832, doi:10.1016/j.cellimm.2012.11.009]
- Duplantier AJ, van Hoek ML. The Human Cathelicidin Antimicrobial Peptide LL-37 as a Potential Treatment for Polymicrobial Infected Wounds. Front Immunol. 2013;4:143. [doi:10.3389/fimmu.2013.00143]
- U.S. Food and Drug Administration. Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act. FDA, Human Drug Compounding (accessed June 2026). [fda.gov]