LL-37: what it is and what the evidence says
An antimicrobial peptide of 37 amino acids that the body makes itself; it opens the membranes of microbes and calls in the cells that defend and repair tissue.
Last reviewed: August 16, 2026 · How we verify this
The ground it plays on
The immune system is not something you turn "up" or "down": it is regulated. A compound that raised the response without control would be a problem, not a benefit, which is why the correct word is modulation. For people with autoimmune or inflammatory conditions, this stops being a technical nuance.
What it is studied for
Ulcer healing, skin defense, mucosal defense.
There is a distinction that almost always gets lost. A compound being studied for something is not the same as achieving it. And even where it works in a dish or in a mouse, that says little about whether it works in a person or whether the benefit is worth the risk. The section below therefore carries more weight than everything above it.
What the human evidence says
In people there are two randomized, placebo-controlled trials, both of local application on venous leg ulcers. The 2014 trial, with 34 participants, showed faster closure with the lower concentrations, and the 2021 phase 2b trial, with 148 participants, saw improvement in the large ulcers but not in the group as a whole.
The limitation that matters most
Trials of injected LL-37 in people are still missing, along with studies in other uses and in pregnancy, breastfeeding, and minors. The laboratory findings on male reproduction and tumor growth have not yet been measured in people.
Regulatory status
Not approved by any regulatory agency. In the United States, the FDA removed it from its Category 2 in April 2026 when its nomination was withdrawn, which does not authorize its compounding in pharmacies. It is not listed by name on the WADA 2026 list, although section S0 covers unapproved substances.
Status can change and varies by country. Always verify the rules in force where you live before drawing conclusions.
Cautions and context
Its effect depends on the amount and the tissue, and in excess it takes part in psoriasis, rosacea, and lupus. With active cancer or a retinal disease that forms new vessels, the decision belongs to the specialist.
With psoriasis, rosacea, lupus, an active infection, pregnancy, or breastfeeding, professional assessment comes before considering it.
What this page cannot give you
A reference page can take you this far. You know what LL-37 is and where its research stands, which already puts you ahead of most readers. Four questions remain that no encyclopedia can answer for you, because the answers depend on your own situation:
- What would you measure beforehand, so that later you could tell whether anything actually changed?
- What would you watch along the way, and how consistently?
- What would you ask a professional, and in how much detail, so you do not walk out with a textbook answer?
- What would make you stop?
That is what the course is for
PeptiXtreme is ${CIF.LECCIONES} lessons that hand out no numbers. Each one ends with your starting point, what to watch along the way, the specific questions you take to a professional and the signals that mean stop. It includes per-module exams, a Certificate of Completion with a verifiable certificate ID, a Progress Tracker to follow how you are doing, and a human advisor you can actually write to.
See the course → Or measure your judgment, freeReferences
Every entry links to its record on PubMed, the US National Library of Medicine database. Open them and check. We would rather have a reader who verifies than one who takes our word for it.
- Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trialhuman Wound Repair Regen · 2014 · PMID 25041740 →
- Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trialhuman Wound Repair Regen · 2021 · PMID 34687253 →
- LL-37: Cathelicidin-related antimicrobial peptide with pleiotropic activityreview Pharmacol Rep · 2016 · PMID 27117377 →
- LL-37, the only human member of the cathelicidin family of antimicrobial peptidesreview Biochim Biophys Acta · 2006 · PMID 16716248 →
- Cathelicidin LL-37: a multitask antimicrobial peptidereview Arch Immunol Ther Exp (Warsz) · 2010 · PMID 20049649 →
- The human cathelicidin LL-37--A pore-forming antibacterial peptide and host-cell modulatorreview Biochim Biophys Acta · 2016 · PMID 26556394 →
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Frequently asked questions
What is LL-37?
An antimicrobial peptide of 37 amino acids that the body makes itself; it opens the membranes of microbes and calls in the cells that defend and repair tissue. It is studied within the area of immune.
Is there human evidence for LL-37?
In people there are two randomized, placebo-controlled trials, both of local application on venous leg ulcers. The 2014 trial, with 34 participants, showed faster closure with the lower concentrations, and the 2021 phase 2b trial, with 148 participants, saw improvement in the large ulcers but not in the group as a whole.
Is it approved by any health agency?
Not approved by any regulatory agency. In the United States, the FDA removed it from its Category 2 in April 2026 when its nomination was withdrawn, which does not authorize its compounding in pharmacies. It is not listed by name on the WADA 2026 list, although section S0 covers unapproved substances.
What is the dose of LL-37?
We do not publish dosages. This is not an oversight. No single figure works for everyone: the regimen depends on a person's medical history, on whatever medication they already take, and on the goal they are chasing, which is something a professional weighs with the case in front of them. What you can build is the ability to walk into that appointment knowing what to ask.
Where can I learn to evaluate this properly?
This page tells you what LL-37 is and what the evidence says. The PeptiXtreme course teaches the other half: what you would measure before considering anything, what you would watch, the specific questions you would take to a professional and when you would stop.