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Human antimicrobial peptide (cathelicidin)

LL-37

LL-37 is a natural 37-amino-acid antimicrobial peptide from human skin, tested on chronic leg and foot ulcers and not approved by the FDA as a drug.

Medical review in progressLast reviewed

US regulatory status

Not approved for human use in the US

LL-37, a natural human antimicrobial peptide, is not approved by the FDA as a drug. As of April 2026 its nomination had been withdrawn from the FDA’s Category 2 safety-risk list, where the FDA noted animal findings of harm to male reproduction and possible tumor-promoting effects in some tissues. It is in no 503A or 503B nomination category. The FDA plans to discuss it with its compounding advisory committee before the end of February 2027.

As of

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On this page
  1. US regulatory status
  2. At a glance
  3. What the research shows
  4. Side effects and safety
  5. Vial math
  6. Questions people ask
  7. Sources
  8. Related compounds

At a glance

Also known as
Cathelicidin LL-37
Supplied as
Freeze-dried powder, mixed before use
Research
Limited human evidence
US status
US status: Not approvedchecked

What the research shows

Evidence grade

Limited human evidence

Some studies in people, but they are small, short, early-phase or uncontrolled.

Every published LL-37 trial applied it to the skin or injected it into tumors; none tested injections under the skin. In the first trial in people, 34 adults with hard-to-heal venous leg ulcers applied LL-37 at one of three strengths or placebo for 4 weeks: at the two lower strengths, healing rate constants were about six and three times higher than placebo and mean ulcer area fell 68% and 50%, while the highest strength did no better than placebo. A larger phase IIb trial (HEAL LL-37, sponsored by Promore Pharma) in 148 people with venous leg ulcers found no significant improvement in healing with LL-37 over placebo across the whole study; a benefit in wounds of 10 cm² or larger came from a post hoc analysis, so it is a hypothesis to test, not a finding. In a 4-week trial of LL-37 cream in mildly infected diabetic foot ulcers, granulation (a measure of new healing tissue) increased more than with placebo cream at every weekly check, but LL-37 did not lower inflammation markers or bacteria counts. An early-phase melanoma trial at MD Anderson that injected it into skin tumors enrolled 4 people.

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How we grade evidence

  1. Strong human evidence

    Consistent results from large randomized controlled trials in people.

  2. Limited human evidence · this page

    Some studies in people, but they are small, short, early-phase or uncontrolled.

  3. Mixed evidence

    Studies in people disagree, or strong evidence for one use sits beside weak evidence for another.

  4. Animal or lab studies only

    Studied in cells or animals, not properly in people. Animal results may not apply to humans.

The grade describes how much research exists and in whom. It is not a judgment that a compound works or is safe.

Side effects and safety

On the skin, LL-37 raised no local or systemic safety concerns in the first venous leg ulcer trial and was well tolerated at both strengths in the phase IIb trial. In the melanoma trial, a 63-year-old woman developed multiple warty bumps and a blistering lesion on her trunk and limbs about 45 days after starting weekly injections into her tumors; biopsies showed atypical skin-cell growth with keratoacanthoma-like features, and all lesions cleared within 2 months of stopping. The FDA says compounded LL-37 may pose a risk of immune reactions for certain routes, may have complexities with peptide-related impurities, and that the agency lacks enough safety information to know whether it would cause harm in people. It adds that nonclinical research suggests harm to male reproduction and that LL-37 “can be protumorigenic in some tissues”. No published trial has tested injections under the skin, so there are no human safety data for that use.

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Vial math

Pre-filled calculators turn your vial, water and prescribed dose into syringe units.

Calculator

These pages do the arithmetic for a vial you already have. They don’t suggest a dose.

This is arithmetic, not medical advice. Confirm with your prescriber or pharmacist.

Questions people ask

What is LL-37?

A peptide your own body makes. LL-37 is a naturally occurring 37-amino-acid peptide that is part of the innate immune system in human skin, and it acts as an antimicrobial peptide. The FDA calls it “Cathelicidin LL-37”. As a drug, it has been tested only as a cream or gel on chronic wounds and as an injection into melanoma skin tumors.

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Is LL-37 FDA approved?

No. No LL-37 product is approved by the FDA. Its nomination for compounding was withdrawn from the FDA’s Category 2 safety-risk list by April 2026, and it is in no 503A or 503B category. The FDA has scheduled it, with GHK-Cu, dihexa, melanotan II and PEG-MGF, for its Pharmacy Compounding Advisory Committee before the end of February 2027, to consider adding it to the 503A bulks list. No briefing document has been posted yet. The committee’s advice is not binding: the FDA generally follows it but is not legally bound to.

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Does LL-37 help wounds heal?

The trials disagree. In a 34-person trial in venous leg ulcers, the two lower strengths shrank ulcers more than placebo over 4 weeks, but the highest strength did not. A larger 148-person phase IIb trial found no significant improvement in healing across the whole group. In diabetic foot ulcers, LL-37 cream increased healing tissue more than placebo cream over 4 weeks but did not reduce bacteria. All of these trials put LL-37 directly on the wound.

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What are the side effects of LL-37?

Applied to ulcers, it was well tolerated in trials. Injected into melanoma tumors, it caused warty, keratoacanthoma-like skin growths in one reported patient, which cleared within 2 months of stopping. The FDA also points to animal findings of harm to male reproduction and possible tumor-promoting effects in some tissues, and to the risk of immune reactions and impurities in compounded products.

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Is LL-37 used as an injection under the skin?

Not in any published trial. Human studies used it on the skin or injected it into tumors, so nothing is known from trials about injecting it under the skin. If you have an unapproved vial, the reconstitution calculator can do the arithmetic, but no official label sets how it should be mixed, and the contents of unapproved vials are not verified. Talk to a licensed prescriber or pharmacist first.

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Is LL-37 banned in sport?

LL-37 is not named on WADA’s 2026 Prohibited List, but WADA’s S0 rule bans, at all times, any substance with no current approval by a government health authority for human therapeutic use that no other section covers. Athletes should check with their anti-doping organization before using it.

Source

Sources

  1. Drugs@FDA: FDA-Approved DrugsU.S. Food and Drug Administration · Accessed Oct 16, 2026 (opens in a new tab)
  2. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety RisksU.S. Food and Drug Administration, 2026 · Accessed Oct 15, 2026 (opens in a new tab)
  3. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (updated May 14, 2026)U.S. Food and Drug Administration, 2026 · Accessed Oct 15, 2026 (opens in a new tab)
  4. Bulk Drug Substances Nominated for Use in Compounding Under Section 503B of the Federal Food, Drug, and Cosmetic ActU.S. Food and Drug Administration, 2025 · Accessed Oct 16, 2026 (opens in a new tab)
  5. Meeting of the Pharmacy Compounding Advisory Committee (to be held before the end of February 2027)U.S. Food and Drug Administration, 2026 · Accessed Oct 15, 2026 (opens in a new tab)
  6. Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trialWound Repair Regen, 2014 · Accessed Oct 16, 2026 (opens in a new tab)
  7. Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trialWound Repair Regen, 2021 · Accessed Oct 16, 2026 (opens in a new tab)
  8. Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trialArch Dermatol Res, 2023 · Accessed Oct 16, 2026 (opens in a new tab)
  9. Induction of Antitumor Response in Melanoma Patients Using the Antimicrobial Peptide LL37, NCT02225366ClinicalTrials.gov · Accessed Oct 16, 2026 (opens in a new tab)
  10. Dermatologic toxicity from novel therapy using antimicrobial peptide LL-37 in melanoma: A detailed examination of the clinicopathologic featuresJ Cutan Pathol, 2018 · Accessed Oct 16, 2026 (opens in a new tab)
  11. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory CommitteeU.S. Food and Drug Administration, 2026 · Accessed Oct 15, 2026 (opens in a new tab)
  12. World Anti-Doping Code International Standard: Prohibited List 2026World Anti-Doping Agency, 2026 · Accessed Oct 16, 2026 (opens in a new tab)

Related compounds

Guides

Medical review in progressLast reviewed

Every medical and regulatory statement on this page links to a checkable source, listed above. Peptinote does arithmetic and education, not medical advice, and never sells or links to sellers of peptides.

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