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LL-37, the germ-fighting peptide your body already makes: what the wound and cancer trials found, and why FDA wants a closer look

By Peptide Policy Watch staff · Published November 9, 2026 · 7 min read · 12 sources, 12 checked at the source

Every time you get a paper cut, your skin starts making a small defensive peptide called LL-37. It pokes holes in bacteria, calls in immune cells and helps a wound close. So it's easy to see the appeal of a bottled version. The catch is that the same molecule shows up in the wrong places in psoriasis and rosacea, and FDA has listed it among compounding ingredients with safety questions. Here's what the human research actually shows.

Facts are as of November 9, 2026. Sources, with retrieval dates, are at the bottom.

A peptide with two jobs

LL-37 gets its name from its first two amino acids, two leucines, and its length of 37. Researchers place it in the skin's innate immunity, the fast, general-purpose defense that acts before antibodies do. [V] It doesn't only kill germs. It also acts as a signal that recruits and switches on other immune cells. [V]

One finding made it famous outside dermatology. In 2006, a team at UCLA showed that when human immune cells detect bacteria, they use vitamin D to switch on cathelicidin, which then helps kill the tuberculosis germ inside those cells. [V] That's lab research on cells, not a treatment study, but it's why LL-37 comes up in conversations about vitamin D.

The other side of the coin came a year later. A 2007 paper in Nature reported that in psoriasis, LL-37 binds the body's own DNA and turns it into a trigger for an immune alarm signal, which the authors suggested may help drive the disease. [V] Also in 2007, a Nature Medicine study reported that facial skin in people with rosacea carried far more cathelicidin than normal, much of it cut into unusual fragments. [V] Your body clearly needs LL-37. Too much, in the wrong form, seems to be part of the problem in some skin diseases.

Where FDA stands

Approval. There is no FDA-approved medicine containing LL-37. [V] Products sold online under that name have not been reviewed by FDA for quality, safety or effect.

Compounding. FDA keeps a public page of bulk ingredients it believes may present significant safety risks in compounding. Cathelicidin LL-37 sits in the table of substances that were once in category 2 and were later withdrawn by whoever nominated them. [V] FDA's entry raises three concerns in its own words, summarized here: possible immune reactions for some routes, difficulty characterizing the peptide and its impurities, and too little safety information to know whether it would harm people. [V]

The same FDA entry adds that animal and lab research suggests LL-37 can promote tumor growth in some tissues. [V] Those are nonclinical findings, meaning lab and animal work, not evidence of harm in people. Our compounding categories explainer covers what the category tables mean.

The advisory meeting. FDA's Pharmacy Compounding Advisory Committee page lists cathelicidin (LL-37) first among five substances to be discussed for the 503ASection of federal drug law covering compounding by state-licensed pharmacies and doctors, usually for a prescription written for one patient. Glossary entry bulks list, with GHK-Cu, dihexa acetate, melanotan II and PEG-MGF. The page says time and place will be set in the coming months. [V] Our preview of that meeting has the full agenda, and our 503A bulks list explainer shows what a committee vote can and can't do.

The human trials, smallest to largest

Most LL-37 papers are lab or animal studies. The human trials are few, and they're worth reading closely, because the biggest one didn't go the way the small one suggested.

The early wound trial. Swedish researchers tested a topical LL-37 on hard-to-heal leg ulcers caused by poor vein circulation. Over four weeks, the two lower strengths cut average ulcer area by 68% and 50%, and the authors saw no local or bodywide safety concerns. Oddly, the strongest version didn't beat placebo. [V] (Small randomized trial.)

The bigger test. Promore Pharma, which develops LL-37 under the name ropocamptide, ran the follow-up in 148 people at sites in Poland and Sweden, all also getting standard compression therapy. In the full study group, LL-37 did not improve healing compared with placebo. A subgroup with large wounds did better on LL-37, but that was a post hoc analysis, and the authors called for a new trial powered to test it. The drug was well tolerated. [V] Three authors worked for the company at the time. [V] (Randomized phase IIb trial; primary result negative.)

Diabetic foot ulcers. An Indonesian team tested an LL-37 cream on mildly infected diabetic foot ulcers over four weeks. The cream group built up more healing tissue at every check, but inflammation markers and bacteria counts didn't fall more than with placebo. The trial is registered as NCT04098562, which listed a planned 40 participants and was last updated in 2019. [V] (Small randomized trial.)

Melanoma. MD Anderson tested LL-37 given directly into skin tumors by the study team, in four patients. [V] A pathology report from the same center described one patient whose treated tumors shrank but who developed many wart-like and blistering skin lesions about six weeks in. They cleared within two months of stopping. [V] (Single case report within a tiny early trial.)

• 148people in the largest LL-37 trial, which missed its main goal [V]
• 34people in the first wound trial, 2014 [V]
• 0FDA-approved drugs containing LL-37 [V]

Limits and unknowns

• Topical isn't the same as everything else. Every wound trial above used LL-37 on the skin surface. None tells us what happens with other routes, which is exactly where FDA says data are thin. [U] That's our reading of the trial record.
• The positive signals are from small or subgroup results. The 2014 trial and the large-wound subgroup are hypothesis-generating. The only large trial was negative on its main measure. [V]
• The two-sided biology is real. Psoriasis and rosacea research shows that more LL-37 isn't automatically better. [V] Whether that matters for a product applied to a wound is unknown. [U]
• What's in the vial. Products sold outside pharmacies get no FDA quality check, so their content and purity are unknown. Our label decoder explains what "research use only" does and doesn't mean. [U]

What to watch

Two things. First, the advisory meeting. When FDA posts briefing documents, they'll show the agency's full review of LL-37, including the animal findings it only summarizes now. Second, whether Promore or anyone else runs the larger, focused wound trial its 2021 paper called for. Until then, LL-37 sits in an interesting spot: a peptide every person makes, with a real but unfinished human research record. For the wider picture, see our evidence ladder, our guide to reading a trial listing, and the 14-peptide status table.

Sources (retrieved November 9, 2026)

1. FDA, "Certain bulk drug substances for use in compounding that may present significant safety risks," content current as of April 22, 2026 [V] — https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
2. FDA, "Meeting of the Pharmacy Compounding Advisory Committee," content current as of April 15, 2026 [V] — https://www.fda.gov/advisory-committees/pharmacy-compounding-advisory-committee/meeting-pharmacy-compounding-advisory-committee
3. openFDA Drugs@FDA search for cathelicidin, no matching application (checked November 9, 2026) [V] — https://api.fda.gov/drug/drugsfda.json?search=openfda.generic_name:cathelicidin
4. Grönberg A et al., "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;22(5):613-21, PMID 25041740 [V] — https://pubmed.ncbi.nlm.nih.gov/25041740/
5. 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;29(6):938-950, PMID 34687253 [V] — https://pubmed.ncbi.nlm.nih.gov/34687253/
6. Miranda E et al., "Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trial," Arch Dermatol Res 2023;315(9):2623-2633, PMID 37480520 [V] — https://pubmed.ncbi.nlm.nih.gov/37480520/
7. ClinicalTrials.gov, NCT04098562, LL-37 cream in diabetic foot ulcer [V] — https://clinicaltrials.gov/study/NCT04098562
8. ClinicalTrials.gov, NCT02225366, "Intratumoral Injections of LL37 for Melanoma," M.D. Anderson Cancer Center (completed; results posted December 9, 2021) [V] — https://clinicaltrials.gov/study/NCT02225366
9. Dolkar T et al., "Dermatologic toxicity from novel therapy using antimicrobial peptide LL-37 in melanoma," J Cutan Pathol 2018;45(7):539-544, PMID 29665030 [V] — https://pubmed.ncbi.nlm.nih.gov/29665030/
10. Liu PT et al., "Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response," Science 2006;311(5768):1770-3, PMID 16497887 [V] — https://pubmed.ncbi.nlm.nih.gov/16497887/
11. Lande R et al., "Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide," Nature 2007;449(7162):564-9, PMID 17873860 [V] — https://pubmed.ncbi.nlm.nih.gov/17873860/
12. Yamasaki K et al., "Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea," Nat Med 2007;13(8):975-80, PMID 17676051 [V] — https://pubmed.ncbi.nlm.nih.gov/17676051/

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