LL-37

Origin and structure

LL-37 was found by researchers in Stockholm. They first predicted an antibacterial peptide, then called FALL-39, from a gene read out of human bone marrow; in 1996 they described the full gene and isolated the mature peptide from white blood cells. It turned out to be two residues shorter than predicted and was renamed after its first two amino acids, both leucine, and its length: LL-37.

The peptide is the active tail of a larger precursor, hCAP-18 (human cationic antimicrobial protein of 18 kilodaltons), encoded by the CAMP gene, which is the only cathelicidin gene in the human genome. White blood cells store the precursor and release the peptide when they empty their granules; epithelial cells in the skin and other linings make it too. LL-37 itself (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES) carries a net positive charge of +6 and forms a helix. As a drug candidate it was given the non-proprietary name ropocamptide.

How it is thought to work

In the lab LL-37 kills bacteria the way many antimicrobial peptides do: its positive charge draws it to the negatively charged bacterial membrane, where it opens pores and the cell breaks apart. In culture it also prevents biofilms and breaks up established ones. The drawbacks, set out in a 2021 review, are that it loses much of its antibacterial activity at the salt levels of body fluids, is broken down by proteases and is toxic to human cells at higher concentrations, which is why much of the work has moved to modified derivatives.

It is also a signalling molecule. LL-37 attracts immune cells through the formyl-peptide receptor FPR2, and bound to fragments of the body's own DNA it can switch on dendritic cells that produce interferon; that second effect is one way it is thought to feed psoriasis and lupus. In wound models it promotes closure: it speeds healing in animal wounds and in human skin kept alive in the lab, and antibodies that block it slow healing. It is plentiful in fresh wounds but was found to be missing from chronic ones, which is the reasoning behind applying it to hard-to-heal ulcers.

Vitamin D is its best-known switch. The CAMP gene carries a vitamin D response element, so active vitamin D turns it on in immune and skin cells. That element exists in primates but not in mice, so mouse studies cannot model the link. Whether a vitamin D supplement raises LL-37 enough to change infection risk in people is a separate question that these cell studies do not answer.

Is LL-37 approved?

No. LL-37 has no marketing authorisation from the EMA, the FDA or any other regulator, and the EMA has not given it an orphan designation. In the Netherlands it is not a registered medicine and may not be sold as one; it is only available as research material, which is the basis our shop operates on.

The Swedish company Promore Pharma, which ran the large leg-ulcer trial, developed it as ropocamptide. In October 2023 the company went into voluntary liquidation, saying the market made it too hard to raise the money needed to develop ropocamptide, its main remaining asset. Weeks later it announced a reverse takeover by the respiratory-monitoring company PMD Device Solutions, under which its own drug development was discontinued.

In the United States LL-37 was nominated for use by compounding pharmacies, and the FDA placed it in Category 2 of its interim compounding policy, the group of substances that may present significant safety risks. The nomination was later withdrawn; on its safety page, last updated in April 2026, the FDA now lists LL-37 among withdrawn nominations and says it lacks the safety information to know whether it would harm people. The FDA has announced that its Pharmacy Compounding Advisory Committee will discuss whether LL-37 belongs on the 503A bulks list, together with GHK-Cu, dihexa, melanotan II and PEG-MGF, at a meeting before the end of February 2027. The committee gives advice; its vote would not be an approval.

In sport, LL-37 is not named on the WADA Prohibited List, but category S0 covers any pharmacological substance that the list does not otherwise address and that no regulator has approved for human therapeutic use. LL-37 fits that description, and S0 substances are prohibited at all times.

What the research shows

Four human trials have been reported. All are small or early-stage, three tested LL-37 on the skin, and only one tested it by injection:

• First-in-human leg-ulcer trial (Wound Repair Regen 2014): 34 patients in Sweden with hard-to-heal venous leg ulcers, randomised to LL-37 at 0.5, 1.6 or 3.2 mg/mL or placebo, applied twice a week for 4 weeks. Healing-rate constants were about six and three times those on placebo at the two lower strengths, but only the 0.5 mg/mL result was statistically significant (p = 0.003); the highest strength did no better than placebo.
• HEAL LL-37, phase IIb (Wound Repair Regen 2021): 148 patients at 15 sites in Poland and Sweden, randomised to LL-37 at 0.5 or 1.6 mg/mL or placebo twice a week for 13 weeks, on top of compression. Confirmed complete closure was 26.5%, 24.7% and 25.3%: no difference in the full group. A post hoc look at ulcers of 10 cm² or more found closure in 28.1% on 0.5 mg/mL against 8.1% on placebo; that was not the question the trial was designed to answer, and the authors called for a new trial.
• Diabetic foot ulcers (Arch Dermatol Res 2023): 25 patients in Jakarta with mildly infected ulcers, 13 on a cream with 0.5 mg/mL LL-37 and 12 on placebo cream, twice a week for 4 weeks. Granulation tissue grew more on LL-37 at every weekly measurement, while the inflammatory markers IL-1α and TNF-α and the bacterial counts did not differ significantly.
• Melanoma (MD Anderson, NCT02225366): a phase I/II study of LL-37 injected into tumours in or just under the skin once a week for up to 8 weeks, at 250 or 500 µg per tumour. Four patients enrolled and three were treated before it closed in 2020; the results posted in 2021 list no serious adverse events, and the study is far too small to say anything about effect.

Side effects and warnings

On the skin LL-37 was well tolerated. In the 148-patient trial, six adverse events in four patients were judged possibly related to treatment: wound infection and dermatitis in one patient each on 0.5 mg/mL, leg swelling in one patient on 1.6 mg/mL, and a deep phlebitis in one patient on placebo. None of the 12 serious adverse events was attributed to the study drug. In the foot-ulcer trial one of the 13 patients on LL-37 had mild irritant dermatitis, put down to wound fluid rather than the cream.

The concerns lie elsewhere. LL-37 is part of the disease process in psoriasis, where complexes of LL-37 and the body's own DNA activate immune cells, and it has been implicated in lupus, rheumatoid arthritis and atherosclerosis. The FDA adds that it may provoke immune reactions against itself for some routes of administration, and that nonclinical studies suggest harm to male reproduction and a tumour-promoting effect in some tissues.

None of these questions has been studied with LL-37 given into the body as a whole: the only injections in a trial went into the tumours of three patients. The safety of injected LL-37 is therefore unknown, and the identity and purity of research material rest on the batch certificate of analysis.

Frequently asked questions

Is LL-37 legal in the Netherlands?

It is not a registered medicine and may not be sold or promoted for human use. It can be bought and sold as research material, which is the basis for our shop. Our guide on research-use-only products in the Netherlands explains what that status means.

Is LL-37 banned in sport?

WADA does not list it by name. Category S0 bans, at all times, any pharmacological substance that the list does not otherwise address and that no regulator has approved for human therapeutic use, and LL-37 meets that description. See our guide on peptides and the doping list.

Does vitamin D raise LL-37?

In cells, yes: active vitamin D binds a response element in the CAMP gene and switches it on in immune and skin cells, a link that exists in primates but not in mice. Those are cell studies. They do not show how much a supplement changes LL-37 in a person, or whether that changes the risk of infection.

Has LL-37 been tested as an injection?

Only into tumours: a phase I/II study at MD Anderson in Texas treated three melanoma patients with weekly injections into tumours in or just under the skin. No trial has injected it under the skin or into a muscle, so there are no human data on what an injected dose does in the body.

Can LL-37 replace antibiotics?

No. It has never been approved as an antibiotic, and in the lab it loses much of its antibacterial activity at the salt levels of body fluids, is broken down by proteases and is toxic to human cells at higher concentrations. Researchers are working on modified derivatives and delivery systems to get around those problems.

Storage and handling

Store according to product-label instructions and batch handling notes. Lyophilized research peptides are commonly kept dry, protected from light, and handled with clean laboratory technique.

References

Checked against these sources on 28 October 2026.