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Peptide (natural human antimicrobial)Limited humanNot FDA approved

LL-37

Human cathelicidin antimicrobial peptide LL-37

Last reviewed October 27, 2026 · 13 sources · Written for general readers · Compare with another compound →

The bottom line

LL-37 is a natural peptide your body makes to kill germs and steer the immune system. Small trials of LL-37 put on leg ulcers and foot ulcers gave mixed results, and the largest trial missed its main goal. No published study has tested the injections sold online, and FDA has flagged animal findings on male fertility and tumor growth.

Where the evidence stands

What it is

LL-37 is a chain of 37 amino acids that the human body cuts from a larger protein made by the CAMP gene. Its sequence is LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES.[1]

It is the only cathelicidin peptide humans make. It is found in skin, in the lining of the airways and in white blood cells, where it kills bacteria and helps direct the immune response.[1]

Researchers have tested lab made LL-37 as a treatment put on leg ulcers, as a cream for diabetic foot ulcers, and as a swallowed form made by engineered bacteria for COVID-19.[2][3][4]

Name
LL-37 (Human cathelicidin antimicrobial peptide LL-37)
Other names
cathelicidin LL-37, CAMP gene product, hCAP18 fragment
Type
Peptide (natural human antimicrobial)
Sequence
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES

How it works

LL-37 does two jobs at once, which is why it attracted interest, and also why it can cause trouble.

  • It punches holes in bacterial membranes, giving it direct germ killing activity in the lab.[1]
  • It also signals to immune cells and to the cells that rebuild skin, which researchers hoped would speed healing.[1]
  • It can bind the body's own DNA and switch on immune cells that make interferon, a process researchers linked to psoriasis.[5]
  • People with rosacea have unusually high levels of abnormal LL-37 fragments in facial skin, and injecting those fragments into mice caused skin inflammation.[6]

The mechanism is well described, but the same signals that fight germs can also drive inflammation, and whether extra LL-37 helps patients is unsettled.

What the research shows

We keep animal and human evidence apart. A result in animals is a reason to study something in people, not proof that it works in people.

Animal and lab studies

Animal findings raise more safety questions than answers

  • FDA states that nonclinical research suggests harmful effects on male reproduction, and that FDA lacks enough safety information on LL-37.[9]
  • In mice carrying human ovarian tumors, blocking LL-37 reduced tumor growth and the blood vessel network that feeds tumors.[8]
  • In mice, injecting the LL-37 fragments found in rosacea skin increased skin inflammation, and mice unable to make cathelicidin were protected.[6]
  • In lab studies with human immune cells, LL-37 bound to the body's own DNA switched on cells involved in psoriasis.[5]

Limit: FDA summarizes several of these findings without listing the studies, so the size of the risk in people is unclear.

Human studies

A few small trials of creams, gels and a swallowed form

  • Leg vein ulcers, first trial (2014): 34 people had three weeks of dummy treatment, then were randomly given one of three strengths of LL-37 or placebo put on the wound for four weeks, with four weeks of follow up. Ulcers shrank by 68 percent and 50 percent on average with the two lower strengths. The highest strength was no better than placebo. No safety concerns were found.[2]
  • Leg vein ulcers, phase 2b (2021): 148 patients with an average age of about 68 and ulcers that had lasted about 20 months used LL-37 or placebo along with compression bandages. LL-37 did not significantly improve healing in the whole group. An unplanned look at people with the largest wounds suggested benefit, which needs a new trial to confirm. Both strengths were well tolerated.[7]
  • Diabetic foot ulcers (2023): adults in Jakarta with mildly infected foot ulcers used LL-37 cream or placebo cream for four weeks. The LL-37 group had more healthy new tissue at every check from day 7 to day 28, but inflammation markers and bacterial growth were not reduced.[3]
  • COVID-19 (2023): 238 adults in hospital with Omicron swallowed bacteria engineered to make LL-37 or placebo. The virus cleared in about 9.8 days versus 14 days, and no severe side effects were seen, but the trial was open label at one hospital.[4]
  • Injections: we found no published human study of LL-37 given as a shot, which is how it is usually sold online. FDA says it lacks enough safety information to judge the risk.[9]

Limit: Every human study was small or unblinded, used the peptide on the skin or by mouth, and none tested the injections sold online.

Claims check

The most common claims about this compound, and what studies actually found. Verdicts rate the evidence, not whether you should use it.

Heals wounds and ulcers

Mixed results

In a first trial of 34 people with leg vein ulcers, the lowest strength put on the wound shrank ulcers by 68 percent on average, while the highest strength did no better than placebo.[2] A larger trial of 148 patients found no significant healing benefit overall.[7] In a trial of people with mildly infected diabetic foot ulcers, LL-37 cream produced more healthy new tissue in the wound than placebo cream over four weeks.[3]

Kills infections, including resistant bacteria

Only in animals

LL-37 kills bacteria in lab tests.[1] The one human trial that measured germs, in diabetic foot ulcers, found that LL-37 cream did not reduce bacterial growth in the wound more than placebo cream.[3] No trial has tested injected LL-37 against any infection.

Treats COVID-19 and viral infections

Mixed results

In one Chinese trial of 238 adults in hospital with the Omicron variant, those who swallowed bacteria engineered to make LL-37 tested negative for the virus in about 9.8 days, against about 14 days with placebo, and no severe side effects were seen.[4] The trial was at a single hospital and was open label, meaning patients and doctors knew who got what, and it has not been repeated.

Clears skin conditions like acne, rosacea or psoriasis

Not tested

No trial has tested LL-37 as a treatment for these skin conditions. Research points the other way: abnormal LL-37 fragments are raised in rosacea skin and caused skin inflammation in mice, and LL-37 bound to DNA helps trigger the immune reaction behind psoriasis.[6][5]

Fights cancer

Not tested

No published human study has tested LL-37 as a cancer treatment. In mice with human ovarian tumors, blocking LL-37 slowed tumor growth, because LL-37 drew in support cells that feed tumors with blood vessels.[8] FDA also notes that it can promote tumor growth in some tissues.[9]

Known risks and side effects

  • Animal findings on fertility and tumors. FDA cites nonclinical research suggesting harm to male reproduction and tumor promoting effects in some tissues.[9] In mice, LL-37 helped ovarian tumors grow.[8]
  • May worsen inflammatory skin disease. High levels of LL-37 fragments are linked to rosacea, and LL-37 helps trigger the immune reaction in psoriasis.[6][5]
  • Immune reactions and unclear contents. FDA says LL-37 may provoke an immune reaction for some routes of use and that it lacks enough safety information to understand the risks.[9]
  • Side effects seen in trials were few, but routes differ. Wound trials found no safety concerns and the peptide was well tolerated, and the swallowed form caused no severe side effects.[2][7][4] None of these tell you what happens when it is injected.
  • Unregulated products. No LL-37 product is approved and it is not on any FDA list that lets pharmacies compound it, so anything sold online has no assurance of what is in the vial.[10]

Regulatory status

Today: LL-37 is not an approved drug and is not on the FDA list of bulk substances that pharmacies may compound.[10] FDA placed cathelicidin LL-37 in category 2, the significant safety concerns group, in September 2023.[11] That nomination was later withdrawn, and LL-37 now sits in an FDA table of withdrawn nominations that repeats the safety concerns.[9] FDA has announced that its Pharmacy Compounding Advisory Committee will discuss LL-37, along with GHK-Cu, dihexa, melanotan II and PEG-MGF, at a meeting before the end of February 2027.[12] Because it has no approval for human use, it falls under WADA's S0 ban.[13]

  1. First human trial in leg vein ulcers is published, in 34 patients.[2]
  2. A 148 patient phase 2b trial finds no significant healing benefit overall.[7]
  3. Small trials of an LL-37 foot ulcer cream and a swallowed form for COVID-19 are published.[3][4]
  4. FDA places cathelicidin LL-37 in category 2 of the nominated bulk substances list.[11]
  5. FDA lists LL-37 among withdrawn nominations and announces it will go to an advisory committee meeting before the end of February 2027.[9][12]

Sources

  1. UniProt Consortium. Cathelicidin antimicrobial peptide (CAMP), human. UniProtKB entry P49913. UniProt P49913
  2. 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;22(5):613-621. PMID 25041740
  3. Miranda E, Bramono K, Yunir 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
  4. Zhao Y, Zhang H, Zhao Z, et al. Efficacy and safety of Oral LL-37 against the Omicron BA.5.1.3 variant of SARS-COV-2: A randomized trial. J Med Virol. 2023;95(8):e29035. PMID 37605995
  5. Lande R, Gregorio J, Facchinetti V, et al. Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide. Nature. 2007;449(7162):564-569. PMID 17873860
  6. Yamasaki K, Di Nardo A, Bardan A, et al. Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea. Nat Med. 2007;13(8):975-980. PMID 17676051
  7. Mahlapuu M, Sidorowicz A, Mikosinski J, 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
  8. Coffelt SB, Marini FC, Watson K, et al. The pro-inflammatory peptide LL-37 promotes ovarian tumor progression through recruitment of multipotent mesenchymal stromal cells. Proc Natl Acad Sci U S A. 2009;106(10):3806-3811. PMID 19234121
  9. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Content current as of April 22, 2026. FDA safety risks page
  10. U.S. Food and Drug Administration. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (category lists). Updated May 14, 2026. FDA 503A category lists
  11. U.S. Food and Drug Administration. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act. Updated September 29, 2023. FDA document, copy hosted by the Alliance for Pharmacy Compounding. FDA list update, Sept 2023
  12. U.S. Food and Drug Administration. Meeting of the Pharmacy Compounding Advisory Committee (planned before the end of February 2027). Content current as of April 15, 2026. FDA advisory committee page
  13. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. Effective 1 January 2026. WADA 2026 List, S0
Medical disclaimer

This page is educational information only. It is not medical advice and does not replace care from a licensed medical provider. Do not use this page to decide whether to take any substance. Talk to a licensed medical provider first.

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