LL-37

What it is

LL-37 is the mature, active form of the only cathelicidin peptide humans make, and it is part of the innate immune system, the body’s fast, non-specific defense¹¹⁵. The gene produces a 170-amino-acid precursor. Enzymes cut off the front part and release a 37-amino-acid peptide that starts with two leucines, which is where the name comes from¹¹⁶. Neutrophils, a type of white blood cell, store it in granules; skin and airway cells release it into sweat, wound fluid and airway fluid¹¹⁷. It kills bacteria physically, by binding the lipopolysaccharide coat of gram-negative bacteria and forming pores in their membranes¹¹⁸. It also signals to immune cells and to the cells lining blood vessels, and in the laboratory it drives the growth of new blood vessels, which is the rationale behind the wound gel¹⁷. The same peptide is tangled up in disease. In psoriasis it binds a patient’s own DNA and turns it into an interferon trigger, and it acts as a target for the patient’s own T cells¹⁹²⁰. In rosacea, abnormally high levels of cathelicidin peptides inflame the skin²¹. Sellers use the names LL-37, cathelicidin and CAP-18 as if they were the same thing, although CAP-18 strictly refers to the precursor protein¹³²².

A Swedish group cloned the peptide in 1995 from a bone marrow gene library and named it FALL-39, after its first four amino acids and its length¹⁶. A US group independently described the same precursor protein as human CAP18¹⁸. In 1996 the Swedish group showed that this gene is the only cathelicidin in the human genome, and that granulocytes release a 37-amino-acid mature peptide, which they called LL-37¹⁵. Promore Pharma, a Swedish company, developed a synthetic version as a wound gel under the non-proprietary name ropocamptide and ran two trials in hard-to-heal venous leg ulcers²⁴. In October 2023 the company entered voluntary liquidation, then announced a reverse takeover of a medical device business and said its own operations would be discontinued²³. Whether that deal completed, and whether anyone is still developing ropocamptide, we could not verify²³.

Benefits: what the research shows

We found three published controlled human trials of synthetic LL-37. All applied it to the skin for chronic wounds. None tested immunity or the treatment of an infection. The first-in-man trial enrolled 34 patients with hard-to-heal venous leg ulcers, with a 3-week placebo run-in, then 4 weeks of twice-weekly gel at 0.5, 1.6 or 3.2 mg/mL, then 4 weeks of follow-up⁴. Healing rate constants were about six-fold and three-fold placebo at the two lower doses (p = 0.003 and p = 0.088), and mean ulcer area fell 68% and 50%. The highest dose was no better than placebo⁴. The larger follow-up trial, at 15 sites in Poland and Sweden, randomized 149 patients to 13 weeks of twice-weekly gel at 0.5 or 1.6 mg/mL or placebo. It missed its primary endpoint: an estimated 26.5%, 24.7% and 25.3% of ulcers closed (P = 0.4453 and P = 0.5274 against placebo)². A post hoc subgroup with ulcers of 10 cm2 or larger favored the lower dose: 28.1% closed against 8.1% on placebo (P = 0.0458), with a faster healing rate (P = 0.0439)². The tests were one-sided, and those subgroups held only about 21 to 24 patients each². A 25-patient trial in Jakarta tested a 0.5 mg/g cream twice a week for 4 weeks on diabetic foot ulcers, most of them uninfected (17 of 25) and the rest mildly infected. Granulation tissue scores were better on days 7, 14, 21 and 28 (p = 0.031, 0.009, 0.006 and 0.037), but the reduction in wound area was only slightly larger and not significant, and bacterial counts did not differ²⁴. For everything else, we found no human evidence. A ClinicalTrials.gov search on 5 October 2026 found only two registered studies that gave people LL-37 itself³. One was a phase 1/2 study injecting LL-37 into melanoma tumors at one US cancer center; it enrolled 4 patients, completed in 2020 and posted results in 2021²⁵. The other is the Jakarta cream trial²⁶. A 2023 Chinese trial in 238 hospitalized patients with COVID-19 reported faster viral clearance, but it gave live engineered bacteria that make LL-37 in the gut, which is a different product from the peptide sold in vials²⁷. The remaining support is animal and laboratory work: LL-37 protected rats from lethal gram-negative sepsis at 1 mg/kg into a vein²⁸, promoted blood vessel growth in rabbits and in mouse wounds¹⁷, and sped skin healing in mice²⁹. The peptide is also fragile in principle, being cut by the enzyme trypsin, although it stayed intact in chronic wound fluid for up to 24 hours³⁰.

Key human studies

Doses studied

Doses below are what studies used or what a label says. They are not advice, and gray-market products may not contain what their label says.

Routes

• Gel or cream on the skin (the only route with controlled human trials we found)
• Injection into tumors (one small cancer study)
• Injection under the skin (a common gray-market route; no human data found)
• Nasal spray (no human data found)
• By mouth as live engineered bacteria that make it (one trial; a different product)

Every dose studied for LL-37, with sources →

Legal status

United States

LL-37 is not approved by FDA for any use. Searches of FDA’s Drugs@FDA database on 7 October 2026 for the active ingredient names ‘ropocamptide’, ‘cathelicidin’ and ‘LL-37’ each returned no match⁶. FDA lists cathelicidin LL-37 among bulk substances ‘previously in category 2’ that were ‘nominated but withdrawn’, and says it lacks sufficient safety-related information to know whether the drug would cause harm when given to humans⁵. Two studies registered on ClinicalTrials.gov gave LL-37 to people, one of them at a US cancer center under a phase 1/2 protocol³²⁵. In a warning letter dated 10 November 2021 to an Indianapolis clinic, FDA noted that LL-37 was among substances that had not been nominated for the 503A bulks list at that time³⁴.

US pharmacies

Under section 503A, pharmacies may compound only with bulk ingredients that have a USP or NF monograph, are part of an FDA-approved drug or are on FDA’s 503A bulks list. Under an interim policy, FDA also does not intend to act against compounding with substances in its ‘Category 1’⁷. Cathelicidin LL-37 fits none of these routes: it is in no category on FDA’s 503A lists updated 14 May 2026⁷. It was in Category 2 (substances that may pose significant safety risks) until the nominators withdrew their nominations, and FDA now lists it as ‘nominated but withdrawn’⁵. On that page (content current 22 April 2026) FDA says compounded drugs containing cathelicidin LL-37 ‘may pose risk for immunogenicity for certain routes of administration’ and ‘may have complexities with regard to peptide-related impurities and API characterization’. It adds that non-clinical findings ‘suggest detrimental effects on male reproduction and that this drug can be protumorigenic in some tissues’⁵. LL-37 was not one of the seven substances discussed at the Pharmacy Compounding Advisory Committee meeting of 23 July 2026 and 24 July 2026³⁵. FDA says the committee will discuss cathelicidin LL-37, with GHK-Cu, dihexa acetate, melanotan II and PEG-MGF, at a separate meeting before the end of February 2027, listing them as substances ‘being considered for inclusion on the 503A bulks list’⁴⁹. Two law firms reported the same plan in April and July 2026⁸⁹. On 8 October 2026 FDA’s page for the meeting still said its time and place ‘will be scheduled in the coming months’, and a Federal Register search that day found no notice of the meeting, which FDA says it intends to publish³⁶⁴⁹. One of the law firms also stressed that removal from Category 2, announced in April 2026, does not make these substances eligible for compounding⁸.

Other countries

Canada: Health Canada listed LL-37 among roughly 43 unauthorized injectable peptide drugs seized from one online seller, in a notice originally published 1 August 2025. It said injectable peptides are regulated as prescription drugs in Canada, that it had authorized none of the seized products, and that selling unauthorized drugs is illegal³⁷. EU: the two leg-ulcer trials ran in Sweden and Poland under EudraCT registrations, so synthetic LL-37 was studied there as an experimental medicine²⁴. We found no European approval, and the developer reported mid-stage results rather than an approval before entering liquidation²³³⁸. UK: The Guardian reported on 4 April 2026 that the MHRA, the UK medicines regulator, would investigate peptide clinics over health claims³⁹; the UK status of LL-37 itself was not verified. Australia: neither LL-37 nor cathelicidin is named in the Poisons Standard in force from 1 October 2026³²; how Australian law otherwise treats it was not verified.

Sport

LL-37 is not named on WADA’s 2026 Prohibited List, in force now, or on the 2027 List, which takes effect 1 January 2027¹⁰¹¹. Class S0 bans at all times ‘any pharmacological substance which is not addressed by any of the subsequent sections of the List and with no current approval by any governmental regulatory health authority for human therapeutic use’¹⁰. We found no approval of LL-37 as a medicine: FDA’s approvals database returns no match, and the only company known to have developed it reported mid-stage trial results, not an approval⁶³⁸. In our reading it therefore falls under S0. That is our inference, not a WADA ruling. WADA’s explanatory note on the 2027 List, which adds peptides as named examples in S0, warns that a peptide not named on the List ‘may still be prohibited and may be harmful to health’³¹.

LL-37 in the legal tracker →

Quality and the gray market

What testing finds

There is no independent testing of gray-market LL-37 at all. Finnrick, an independent testing service that publishes third-party laboratory results for peptides, showed 0 tests and 0 rated vendors for LL-37 as of 5 October 2026 and stated ‘No published LL-37 tests yet’¹². The two vendors in its LL-37 table had no tests at all¹². For comparison, its default standard elsewhere is at least 99.5% purity with content within 35% of the label⁴³. What sellers publish is not reliable. One vendor’s product page listed a 37-letter sequence that differs from LL-37 at 24 of its 37 positions, and a CAS number that PubChem maps to the amide trifluoroacetate salt rather than the free peptide¹³²². FDA says compounded products containing cathelicidin LL-37 may have complexities with peptide-related impurities and with characterizing the active ingredient⁵. In the trials, by contrast, the product was tested: every batch of the gel used in the 149-person trial held 90% to 110% of its stated content, passed an identity test and had impurities totaling 0.5%², and the foot-ulcer cream, made with purified LL-37 from a UK peptide supplier, had its LL-37 content and stability tested over 12 weeks²⁴.

How it is sold

LL-37 is sold online as freeze-dried powder in vials labeled for research use only, and by clinics as injections and nasal sprays¹³¹⁴. One seller’s page offers a 5 mg vial of freeze-dried powder, claims purity of at least 95% ‘typically verified by HPLC and mass spectrometry’, and says the product ‘is supplied strictly for research purposes’¹³. Community pages overstate what the trials showed. One says that topical synthetic LL-37 ‘significantly accelerated healing rates compared to placebo’ while citing the trial that missed its primary endpoint²⁴¹. Another claims that clinical trials show the peptide ‘heals stubborn wounds six times faster than placebo’; the six-fold figure was a healing rate constant in a 34-patient dose-finding trial, not a healing time, and the larger trial did not confirm it²⁴⁴². Demand looks modest next to the popular repair peptides. On one vendor’s popularity-sorted catalog on 5 October 2026, LL-37 ranked 38th of 41 products¹⁴, and no independent test of it has ever been published¹². Health Canada has seized unauthorized injectable LL-37 sold online³⁷.

Side effects and risks

• Unwanted immune reactions. FDA says compounded drugs containing cathelicidin LL-37 may pose a risk of immunogenicity for certain routes of administration, and that it lacks sufficient safety information to know whether the drug would cause harm in humans⁵.
• Tumor promotion. FDA says non-clinical findings suggest the drug can be protumorigenic in some tissues⁵. Laboratory and animal work supports that for breast, lung and ovarian cancer⁴⁴⁴⁵⁴⁶, while a review of the field notes the opposite effect in colon and gastric cancer⁴⁷.
• Male reproduction. FDA says non-clinical findings suggest detrimental effects on male reproduction⁵. The closest published work we found made sperm immotile and triggered a premature acrosome reaction, and was proposed as a vaginal contraceptive⁴⁰.
• Autoimmune and inflammatory skin disease. LL-37 is part of the biology of psoriasis, where it turns a patient’s own DNA into an immune trigger and serves as a target for their T cells, and of rosacea, where high levels inflame the skin¹⁹²⁰²¹.
• Documented skin toxicity. A melanoma patient given weekly injections into tumors developed multiple atypical squamous skin lesions about 45 days in; they cleared within 2 months of stopping³³. A squamous cell carcinoma was also among the adverse events posted for the 4-patient registry study²⁵.
• The products do not match the evidence. The trials used a gel or cream on open ulcers, and none tested immunity, infection, injections under the skin or nasal sprays²³⁴²⁴.
• Unknown product quality. No independent test results for gray-market LL-37 exist¹², at least one vendor publishes a sequence that is not LL-37¹³, and a 2026 review of peptide use in sport warns that such products are often mislabeled or contaminated⁴⁸.
• Anti-doping. LL-37 is not named on WADA’s Lists, but by our reading it falls under class S0, which is banned at all times¹⁰¹¹. WADA warns that peptides not named on the List ‘may still be prohibited’³¹.
• Legal. US pharmacies have no lawful route under section 503A to compound it⁷, and Health Canada has seized unauthorized injectable LL-37³⁷.

Documented harms

• Jul 2018A case report described a 63-year-old woman with advanced melanoma who developed multiple wart-like papules and a blistering lesion about 45 days into weekly injections of LL-37 into her tumors. Eleven of twelve biopsies showed atypical squamous proliferation. All lesions resolved within two months of stopping³³.
• 9 Dec 2021Results posted for the 4-patient melanoma study list one squamous cell carcinoma, one actinic keratosis, anemia, low lymphocyte and white cell counts, low thyroid function and raised bilirubin among adverse events. No deaths and no serious adverse events were reported²⁵.
• 1 Aug 2025Health Canada named LL-37 among roughly 43 unauthorized injectable peptide drugs it seized from one online seller, warning that such products may pose serious health risks. The notice reports no case of harm from LL-37 itself³⁷.

Questions people ask

What is still unknown

• Whether lab-made LL-37 does anything for immunity or for treating an infection in people. We found no trial of it as a general immune booster or a treatment for infection.
• Whether the large-ulcer finding in the 149-patient trial is real. It was a post hoc subgroup of about 21 to 24 patients per arm, analyzed with one-sided tests, after the main result was negative.
• Whether anyone is still developing ropocamptide. The developer entered voluntary liquidation in October 2023 and announced a reverse takeover; we could not verify that the deal completed.
• What evidence FDA relies on for its statements about male reproduction and tumor promotion. Its safety-risk page cites no studies, and the closest published work we found is a contraceptive study in mice and human sperm samples.
• Whether the 2018 skin toxicity case report describes a patient from the registered melanoma study. The design and timing match, but neither document says so.
• Why the melanoma registry record lists enrollment of 4 while the posted tables show 3 patients starting treatment, and why its outcome tables are ambiguous.
• Why the registry record for the Jakarta cream trial (status unknown, 40 patients planned, 0.5 mg/mL) does not match the published paper (25 patients, 2020 to 2021, 0.5 mg/g). The record was last updated 25 September 2019.
• When FDA’s compounding advisers will meet on LL-37, and what FDA will then decide. FDA has said only that the meeting will be before the end of February 2027, and had set no date by 8 October 2026.
• Whether LL-37 was ever formally nominated for the 503A bulks list. FDA’s safety-risk page lists it as ‘nominated but withdrawn’, while an FDA warning letter of 10 November 2021 said it had not been nominated.
• What is actually in gray-market LL-37 vials. No independent testing has been published.
• How long LL-37 lasts in the body by any route. We found no human pharmacokinetic study.
• The legal status of LL-37 in the UK, the EU and Australia beyond the checks reported above.

Sources

1. 1CAMP_HUMAN (P49913): Cathelicidin antimicrobial peptide, including antibacterial peptide LL-37 (residues 134-170) UniProt Consortium, 2 Sep 2026. uniprot.org
2. 2Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trial Wound Repair and Regeneration, Nov 2021. pubmed.ncbi.nlm.nih.gov
3. 3ClinicalTrials.gov intervention search for ‘LL-37’ (20 records; only two gave LL-37 to people) ClinicalTrials.gov, accessed 5 Oct 2026. clinicaltrials.gov
4. 4Treatment 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 and Regeneration, Sep 2014. pubmed.ncbi.nlm.nih.gov
5. 5Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks U.S. Food and Drug Administration, 22 Apr 2026. fda.gov
6. 6Drugs@FDA API searches for the active ingredient names ‘ropocamptide’, ‘cathelicidin’ and ‘LL-37’ (no matches) U.S. Food and Drug Administration (openFDA), accessed 7 Oct 2026. api.fda.gov · data query
7. 7Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act (categories list) U.S. Food and Drug Administration, 14 May 2026. fda.gov
8. 8FDA to Remove 12 Popular Peptides from the Category 2 ‘Do Not Compound’ List Frier Levitt, 16 Apr 2026. frierlevitt.com
9. 9Bulk-list bound? PCAC backs majority of peptides in two-day public meeting McDermott Will & Schulte, 27 Jul 2026. mcdermottlaw.com
10. 10World Anti-Doping Code International Standard: Prohibited List 2026 World Anti-Doping Agency, 24 Sep 2025. wada-ama.org
11. 11World Anti-Doping Code International Standard: Prohibited List 2027 World Anti-Doping Agency, 21 Sep 2026. wada-ama.org
12. 12LL-37: safety testing results and vendor ratings (no published tests) Finnrick, accessed 5 Oct 2026. finnrick.com
13. 13LL37 5mg product page (research peptide seller; sequence, CAS number and purity claims) Medica Depot (vendor), accessed 5 Oct 2026. medicadepot.com (seller page, deliberately not linked)
14. 14Shop, sorted by popularity, page 3 of 3 (research peptide vendor catalog; LL-37 listing) Ascension Peptides (vendor), accessed 5 Oct 2026. ascensionpeptides.com (seller page, deliberately not linked)
15. 15The human gene FALL39 and processing of the cathelin precursor to the antibacterial peptide LL-37 in granulocytes European Journal of Biochemistry, 1 Jun 1996. pubmed.ncbi.nlm.nih.gov
16. 16FALL-39, a putative human peptide antibiotic, is cysteine-free and expressed in bone marrow and testis Proceedings of the National Academy of Sciences, 3 Jan 1995. pubmed.ncbi.nlm.nih.gov
17. 17An angiogenic role for the human peptide antibiotic LL-37/hCAP-18 The Journal of Clinical Investigation, Jun 2003. pubmed.ncbi.nlm.nih.gov
18. 18Human CAP18: a novel antimicrobial lipopolysaccharide-binding protein Infection and Immunity, Apr 1995. pubmed.ncbi.nlm.nih.gov
19. 19Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide Nature, 4 Oct 2007. pubmed.ncbi.nlm.nih.gov
20. 20The antimicrobial peptide LL37 is a T-cell autoantigen in psoriasis Nature Communications, 3 Dec 2014. pubmed.ncbi.nlm.nih.gov
21. 21Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea Nature Medicine, Aug 2007. pubmed.ncbi.nlm.nih.gov
22. 22Cathelicidin LL-37 (ropocamptide), CID 16198951 PubChem, U.S. National Library of Medicine, accessed 5 Oct 2026. pubchem.ncbi.nlm.nih.gov
23. 23Promore Pharma AB intends to carry out a reverse acquisition of PMD Device Solutions AB ACCESS Newswire, via Yahoo Finance, 29 Nov 2023. finance.yahoo.com
24. 24Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trial Archives of Dermatological Research, Nov 2023. pubmed.ncbi.nlm.nih.gov
25. 25Intratumoral Injections of LL37 for Melanoma (NCT02225366), registry record with posted results ClinicalTrials.gov, 9 Dec 2021. clinicaltrials.gov
26. 26The Efficacy of LL-37 Cream in Diabetic Foot Ulcer (NCT04098562), registry record ClinicalTrials.gov, 25 Sep 2019. clinicaltrials.gov
27. 27Efficacy and safety of oral LL-37 against the Omicron BA.5.1.3 variant of SARS-CoV-2: A randomized trial Journal of Medical Virology, Aug 2023. pubmed.ncbi.nlm.nih.gov
28. 28LL-37 protects rats against lethal sepsis caused by gram-negative bacteria Antimicrobial Agents and Chemotherapy, May 2006. pubmed.ncbi.nlm.nih.gov
29. 29Wound healing activity of the human antimicrobial peptide LL37 Peptides, Jul 2011. pubmed.ncbi.nlm.nih.gov
30. 30Stability of the cathelicidin peptide LL-37 in a non-healing wound environment Acta Dermato-Venereologica, Sep 2011. pubmed.ncbi.nlm.nih.gov
31. 31Summary of Major Modifications and Explanatory Notes: 2027 Prohibited List World Anti-Doping Agency, 21 Sep 2026. wada-ama.org
32. 32Therapeutic Goods (Poisons Standard—October 2026) Instrument 2026 (F2026L01327) Federal Register of Legislation, Australian Government, 28 Sep 2026. legislation.gov.au
33. 33Dermatologic toxicity from novel therapy using antimicrobial peptide LL-37 in melanoma: A detailed examination of the clinicopathologic features Journal of Cutaneous Pathology, Jul 2018. pubmed.ncbi.nlm.nih.gov
34. 34Warning letter to Advanced Nutriceuticals, LLC dba The Guyer Institute of Molecular Medicine (MARCS-CMS 615908) U.S. Food and Drug Administration, 10 Nov 2021. fda.gov
35. 35July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee U.S. Food and Drug Administration, 6 Aug 2026. fda.gov
36. 36Federal Register search: FDA documents mentioning “Pharmacy Compounding Advisory Committee” published since 1 April 2026 Federal Register, accessed 8 Oct 2026. federalregister.gov
37. 37Unauthorized injectable peptide drugs seized and sold by Canada Peptide may pose serious health risks (RA-77807) Health Canada, 1 Aug 2025. recalls-rappels.canada.ca
38. 38Promore Pharma reports positive results from Phase IIb study of ropocamptide (LL-37) in venous leg ulcers Nasdaq News (company announcement), 19 Nov 2020. view.news.eu.nasdaq.com
39. 39Medicines watchdog to investigate UK peptide clinics over health claims The Guardian, 4 Apr 2026. theguardian.com
40. 40Antimicrobial host defence peptide, LL-37, as a potential vaginal contraceptive Human Reproduction, Apr 2014. pubmed.ncbi.nlm.nih.gov
41. 41LL-37 5 mg vial: dosage protocol PeptideDosages.com, 20 Sep 2026. peptidedosages.com
42. 42LL-37 Dosage, Safety & Stacks Peptide Initiative, 10 Aug 2026. peptideinitiative.com
43. 43Methodology Finnrick, accessed 5 Oct 2026. finnrick.com
44. 44Human antimicrobial protein hCAP18/LL-37 promotes a metastatic phenotype in breast cancer Breast Cancer Research, 2009. pubmed.ncbi.nlm.nih.gov
45. 45The host defence peptide LL-37/hCAP-18 is a growth factor for lung cancer cells Lung Cancer, Jan 2008. pubmed.ncbi.nlm.nih.gov
46. 46The pro-inflammatory peptide LL-37 promotes ovarian tumor progression through recruitment of multipotent mesenchymal stromal cells Proceedings of the National Academy of Sciences, 10 Mar 2009. pubmed.ncbi.nlm.nih.gov
47. 47The Role of Cathelicidin LL-37 in Cancer Development Archivum Immunologiae et Therapiae Experimentalis, Feb 2016. pubmed.ncbi.nlm.nih.gov
48. 48A new era of doping? Use of peptide and peptide-analog drugs in recreational and professional sport and bodybuilding: a critical review The Journal of Sports Medicine and Physical Fitness, Jul 2026. pubmed.ncbi.nlm.nih.gov
49. 49Meeting of the Pharmacy Compounding Advisory Committee (to be held before the end of February 2027) U.S. Food and Drug Administration, 15 Apr 2026. fda.gov