LL-37: uses, evidence and status | Inside Your Peptides

compound file

The answer, first. The only human cathelicidin, a 37-residue peptide cut from the hCAP-18 precursor by neutrophils and skin, described in the 1990s. The strongest evidence is for bacterial killing, graded D — animal or mechanism only.

Minimum inhibitory concentration under 10 micrograms per millilitre against Pseudomonas, Salmonella, Escherichia coli, Listeria, staphylococci and vancomycin-resistant enterococci, even at 100 millimolar sodium chloride ³.

Broth assays, no infection model in a person. Every other use — skin re-epithelialisation, innate host defence, injected immune support, hard-to-heal leg ulcers — grade D or E: animal or mechanism data only, or a claim the human trials have already tested and not supported.

What it is used for

Every use graded on its own evidence, not the compound as a whole. 5 outcomes, ranked by what the human record supports.

#outcome · human · animal · gradewhat the best evidence actually shows

01Bacterial killingno infection trial · in vitro onlygrade DMinimum inhibitory concentration under 10 micrograms per millilitre against Pseudomonas, Salmonella, Escherichia coli, Listeria, staphylococci and vancomycin-resistant enterococci, even at 100 millimolar sodium chloride ³. Broth assays, no infection model in a person.

02Skin re-epithelialisationtissue findings, no outcome trial · cell and organ culturegrade DLL-37 is upregulated in healing human skin wounds and absent from chronic ulcer epithelium, and blocking it inhibits re-epithelialisation in culture ⁴⁵. Human tissue, not a human outcome.

03Innate host defence1 deficiency cohort · supporting mouse workgrade DPapillon-Lefevre patients cannot process hCAP-18 into LL-37 and lose periodontal tissue early, which shows the endogenous peptide matters ⁶. Deficiency evidence, not a trial of administering it.

04Injected immune supportzero trials of any design · nonclinical safety signalsgrade DNo human trial of injected LL-37 exists for any indication. FDA cites nonclinical findings of detrimental effects on male reproduction and protumorigenic activity in some tissues ⁸.

05Hard-to-heal leg ulcers2 RCTs, the larger null · rodent wound modelsgrade ETwo randomised trials, the only human efficacy data for any LL-37 product. The 34-patient first-in-man found a six-fold healing rate constant at 0.5 mg/mL, P=0.003 ¹. The 148-patient phase 2b was null ².

gradewhat it means

ARegulatory approval, or multiple adequately-powered trials agreeing with each other

BAt least one well-powered human randomised trial, with the direction replicated

CSmall or open-label human trials only

DAnimal or mechanism data only, with no controlled human outcome

EA claim the human trials have already killed

How it works

The proposed mechanism, in three steps. A mechanism is a reason to run a trial, never a substitute for one.

1targethCAP-18 sits in neutrophil granules and is cleaved outside the cell by proteinase 3 to release the 37-residue peptide ⁷.

2signalThe cationic alpha-helix binds lipopolysaccharide with high affinity and permeabilises both the outer and inner bacterial membrane ³.

3effectIt also carries self-DNA and self-RNA into dendritic cells, which is how it drives interferon in lupus and psoriasis ⁹¹⁰¹².

What it does not do

Claims the current record does not support. Worth knowing before you set expectations.

not supported by the evidence

LL-37 clears chronic infection or biofilm. No human infection trial of any design exists. The killing data are broth assays, and salt blunts them against several organisms ³.
Injecting LL-37 boosts immunity. No trial. FDA lists nonclinical findings of harm to male reproduction and protumorigenic effects in some tissues ⁸.
It is safe because it is human. It is the autoantigen that LL-37-specific T cells recognise in psoriasis, and it drives interferon in lupus ⁹¹⁰.
Topical LL-37 heals leg ulcers. The 148-patient randomised trial found no significant benefit over placebo on the full study population ².

How it is used

What published protocols administered, and what the community reports doing. Descriptive on both counts, and never a recommendation.

routeReported subcutaneous and nebulised. Every human trial applied a topical gel to the wound bed, twice weekly, under compression.

formatLyophilised powder in a vial. The trial product was a hydrogel, developed as ropocamptide.

published dosesThe trials applied topical LL-37 at 0.5, 1.6 and 3.2 mg per millilitre twice weekly for four weeks ¹². The 3.2 mg per millilitre arm performed no better than placebo, so the phase 2b carried only the two lower strengths ¹². No injectable dose has been published in any human.

human pharmacokineticsNo human pharmacokinetic data published for administered LL-37.

reported conventionsAs reported on peptide and chronic-illness forums, 2019 to 2026: subcutaneous doses of roughly 100 micrograms to 1 milligram. Courses run one to four weeks rather than continuously. Convention, not guidance.

commonly paired withThymosin Alpha-1

This site does not publish protocols to follow. The doses above are what studies administered or what users report, stated as facts about the literature and the market. How protocols are structured, mixing and storage and the reconstitution calculator cover the arithmetic.

What to expect

Where a trial measured it, the trial. Where only the community reports it, that is said out loud.

onsetThe first-in-man trial ran a four-week treatment phase and a four-week follow-up ¹. Its effect showed up in the healing rate constant rather than at a single timepoint ¹. As reported for injected use: days. No trial measured that.

most common reportAs reported: nothing clearly attributable. The endpoints that moved in the trials were wound-area measurements, not sensations ¹.

adverse effectsBoth randomised trials reported LL-37 was safe and well tolerated with no local or systemic safety concerns, across 34 and 148 patients ¹². As reported for injection: site pain and flu-like symptoms. FDA flags nonclinical reproductive and protumorigenic findings ⁸.

the stop signalAs reported: the end of a short course. Both published trials stopped at four weeks by protocol, not on any signal from the patient ¹².

Approval and status

What regulators and sport bodies have actually said, separately from what the evidence shows.

approvalNot approved anywhere. Developed as ropocamptide and taken to phase 2b in venous leg ulcers.

FDACategory 2 on FDA's compounding safety-risk list as cathelicidin LL-37, citing immunogenicity plus nonclinical reproductive and protumorigenic findings ⁸.

sport [WADA]Not named. S0 catches any non-approved substance ¹¹.

sold asresearch chemical

Check the vial

The grade above describes a molecule studied under controlled conditions. It says nothing about the powder in a particular vial.

That gap is the one part of this market a reader can actually close. How to read a certificate of analysis covers the five measures in five minutes, and the 2026 audit grades vendors on the documents they publish against a rubric printed in full.

Questions we get

What is LL-37 used for?

It is sold for immune support, chronic infection and biofilm. The actual human record is narrower, and it points elsewhere. Two randomised trials of a topical gel on hard-to-heal venous leg ulcers, run by a Swedish drug developer under the name ropocamptide.

Everything else is laboratory work. It kills a broad range of bacteria on a culture plate, it rises in healing human skin, and it is missing from chronic ulcer epithelium.

How is LL-37 used?

Descriptively. The published human protocol is a topical hydrogel at 0.5, 1.6 or 3.2 milligrams per millilitre. It went on the wound bed twice weekly for four weeks, alongside compression.

The highest strength did no better than placebo and was dropped from the larger trial. As reported on forums between 2019 and 2026, the convention for the vialled powder is subcutaneous, roughly 100 micrograms to 1 milligram, in short courses.

How long does LL-37 take to work?

The trials treated for four weeks and followed for four more. In the first-in-man study the signal appeared as a faster healing rate constant across that window rather than at one timepoint.

In the larger phase 2b there was no signal to time. No trial has ever measured onset for injected LL-37, because no trial of injected LL-37 exists. As reported, users describe effects within days.

Did the LL-37 leg ulcer trials work?

The first one looked like it did and the second one did not. In 34 patients, healing rate constants at 0.5 and 1.6 milligrams per millilitre ran roughly six-fold and three-fold above placebo. Mean ulcer area fell 68% at the low dose.

The 148-patient phase 2b then found no significant improvement over placebo. A post hoc subgroup with wounds of at least 10 square centimetres did separate, which the authors called an observation needing a properly powered trial.

References

Gronberg A, Mahlapuu M, Stahle M, Whately-Smith C, Rollman O. Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial. Wound Repair Regen. 2014. PMID 25041740
Mahlapuu M, et al. Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial. Wound Repair Regen. 2021. PMID 34687253
Turner J, Cho Y, Dinh NN, Waring AJ, Lehrer RI. Activities of LL-37, a cathelin-associated antimicrobial peptide of human neutrophils. Antimicrob Agents Chemother. 1998. PMID 9736536
Heilborn JD, et al. The cathelicidin anti-microbial peptide LL-37 is involved in re-epithelialization of human skin wounds and is lacking in chronic ulcer epithelium. J Invest Dermatol. 2003. PMID 12603850
Carretero M, et al. In vitro and in vivo wound healing-promoting activities of human cathelicidin LL-37. J Invest Dermatol. 2008. PMID 17805349
Lack of cathelicidin processing in Papillon-Lefevre syndrome patients reveals essential role of LL-37 in periodontal homeostasis. Orphanet J Rare Dis. 2014. PMID 25260376
Sorensen OE, et al. Human cathelicidin, hCAP-18, is processed to the antimicrobial peptide LL-37 by extracellular cleavage with proteinase 3. Blood. 2001. PMID 11389039
FDA. Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks. Content current as of 22 April 2026. fda.gov
Lande R, et al. The antimicrobial peptide LL37 is a T-cell autoantigen in psoriasis. Nat Commun. 2014. PMID 25470744
Lande R, et al. Neutrophils activate plasmacytoid dendritic cells by releasing self-DNA-peptide complexes in systemic lupus erythematosus. Sci Transl Med. 2011. PMID 21389263
World Anti-Doping Agency. The Prohibited List, section S0 Non-Approved Substances. wada-ama.org
Immunomodulatory role of the antimicrobial LL-37 peptide in autoimmune diseases and viral infections. Vaccines. 2020. PMID 32927756

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