LL-37 peptide: what it is, what the trials found and what is unknown

LL-37 is part of the body’s innate immune defences. In 1995 researchers at Stockholm University found a human bone-marrow gene sequence coding for a putative antibacterial peptide they named FALL-39, after its first four amino acids and its length ^[1]. In 1996 the same group showed that the mature peptide found in white blood cells (granulocytes) is 37 amino acids long and begins with two leucines, hence LL-37, and that it is the only cathelicidin gene in the human genome ^[2].

LL-37 is released from a larger precursor protein called hCAP18. It is made by white blood cells and by the lining cells of the skin, gut and airways, and it forms an amphipathic helix with broad antimicrobial activity ^[3]. Research peptide suppliers sell synthetic LL-37, which is identical in sequence to the natural peptide. It is sometimes grouped with other peptides studied for inflammation, such as KPV and thymosin alpha-1, although they work in different ways.

The name is written several ways: LL-37, LL 37 and LL37 all refer to the same peptide, and cathelicidin LL-37 or human cathelicidin are its formal descriptions. Because LL-37 is a natural human peptide, much of what is known about it comes from studying people who make too much or too little of it, rather than from giving it as a drug.

The body’s production of cathelicidin is linked to vitamin D. A 2006 Science study found that when immune cells called macrophages detect bacteria through Toll-like receptors, they switch on genes for the vitamin D receptor and for the enzyme that activates vitamin D, which in turn induces cathelicidin and helps kill the tuberculosis bacterium inside the cells. Blood serum with low vitamin D levels was less able to support this cathelicidin response ^[11].

This is one reason LL-37 comes up in discussions of vitamin D and infection. It is a finding about the body’s own production of the peptide. It does not show that taking vitamin D or injecting synthetic LL-37 prevents infection.

Beyond killing microbes directly, LL-37 influences the immune system: it binds and neutralises bacterial endotoxin (LPS), attracts immune cells to sites of injury or infection, and promotes re-growth of skin over wounds ^[3]. These signalling roles cut both ways. A 2007 Nature study found that LL-37 binds the body’s own DNA released from damaged cells and turns it into a trigger for interferon production by plasmacytoid dendritic cells, a pathway the authors proposed drives inflammation in psoriasis ^[4]. Another 2007 study found abnormally high levels of cathelicidin, and abnormally processed forms of it, in the facial skin of people with rosacea, and showed that these peptides increased skin inflammation when injected into mice ^[5].

LL-37’s role in cancer is also two-sided. A 2016 review reported that high levels of LL-37 have been linked with the growth of ovarian, lung and breast cancers, but with suppression of tumours in the colon and stomach ^[9].

Against bacteria growing in biofilms, the slimy communities behind many chronic infections, LL-37 acts at lower concentrations than it needs to kill free-floating bacteria. In a 2008 laboratory study, it prevented Pseudomonas aeruginosa from forming biofilms at 0.5 µg/mL, while the concentration needed to stop the bacteria growing was 64 µg/mL; it also affected biofilms that had already formed ^[15].

Most claims about LL-37 peptide benefits draw on its natural roles in infection defence and wound repair. The strongest evidence for those roles comes from studies of human tissue and of people with too little of it, not from treatment trials.

Wound healing: a 2003 study found that the precursor hCAP18 rises sharply in human skin after wounding, peaking at 48 hours, and is present in the skin cells migrating over the wound. In chronic leg ulcers it was low and absent from the ulcer edge. In cultured human skin, blocking LL-37 with antibodies stopped the wound re-covering with skin, which suggests LL-37 is needed for normal wound closure ^[14]. This work is the rationale for the leg ulcer trials described below.

Deficiency: people with morbus Kostmann, a severe inherited lack of neutrophils, still have recurrent infections and severe gum disease despite treatment that restores their neutrophil counts. A 2002 Lancet study found that their neutrophils lacked the LL-37 precursor and that no LL-37 precursor could be detected in their plasma or saliva; the one patient who had had a bone-marrow transplant had near-normal LL-37 and normal teeth and gums ^[12]. In atopic eczema, a 2002 study found LL-37 and another antimicrobial peptide were significantly lower in skin lesions than in psoriasis, which may help explain why eczema skin is prone to Staphylococcus aureus infection ^[13].

Excess: as described above, too much LL-37 activity is linked to psoriasis and rosacea ^{[4] [5]}. The same peptide that is missing in eczema and Kostmann disease is overactive in these conditions, which is why the effect of giving extra LL-37 cannot be predicted from its natural role alone.

Venous leg ulcers, first-in-human trial: 34 people with hard-to-heal venous leg ulcers applied LL-37 at 0.5, 1.6 or 3.2 mg/mL, or placebo, twice weekly for four weeks. The two lower concentrations were associated with markedly faster healing (healing rate constants about six- and three-fold higher than placebo), while the highest concentration was no better than placebo. There were no local or systemic safety concerns ^[6].

Venous leg ulcers, phase 2b: a larger follow-up trial (HEAL LL-37) randomised 148 patients across Poland and Sweden to LL-37 at 0.5 or 1.6 mg/mL or placebo, alongside compression therapy. It found no significant improvement in healing in the whole study population. A post hoc analysis suggested possible benefit in patients with wounds of at least 10 cm², which the authors said needs a properly powered trial. The drug was well tolerated at both strengths. The trial was run by the company developing LL-37 under the name ropocamptide ^[7]. That company is Promore Pharma of Stockholm, and the published trial report is the main public source for the HEAL LL-37 results ^[7].

Diabetic foot ulcers: in a randomised, double-blind trial in Jakarta, run from 2020 to 2021, people with mildly infected diabetic foot ulcers applied LL-37 cream or placebo cream twice a week for four weeks. The LL-37 group had a consistently greater increase in healthy granulation tissue at days 7, 14, 21 and 28, but LL-37 did not reduce the inflammatory markers IL-1α and TNF-α or bacterial counts compared with placebo ^[16]. The registry entry for this trial describes 0.5 mg/mL LL-37 cream and a planned 40 participants ^[18].

Melanoma: LL-37 has been injected directly into tumours in a phase 1 trial for melanoma skin metastases. A 2018 case report from that programme described a patient who developed multiple wart-like and blistering skin lesions after eight weekly injections; the lesions resolved within two months of stopping ^[8]. The trial’s registry entry, at MD Anderson Cancer Center, lists it as completed with four participants enrolled ^[17].

In summary, the LL-37 clinical trials status as of September 2026 is: two published leg ulcer trials (one positive and small, one negative overall), one published diabetic foot ulcer trial reporting improved granulation, and one small intratumoral melanoma study. All used LL-37 on or in a lesion. None tested LL-37 injected under the skin for general health.

In the trials, effects were measured over weeks of treatment. The first leg ulcer trial treated patients for four weeks ^[6], and the diabetic foot ulcer trial measured wounds weekly and saw differences in granulation tissue from day 7 ^[16]. These are wound-healing timelines for topical treatment of ulcers and say nothing about how long injected LL-37 bought online might take to have any effect.

In the leg ulcer trials, LL-37 was applied to the wound at concentrations of 0.5, 1.6 or 3.2 mg/mL twice weekly in the first trial ^[6], and at 0.5 or 1.6 mg/mL in the phase 2b trial ^[7]. Notably, 3.2 mg/mL was no more effective than placebo in the first trial ^[6]. These were topical applications to wounds; no published trial has established a dose for LL-37 injected under the skin, and these figures are not recommendations. For converting vial contents to concentrations, see the peptide calculator.

The diabetic foot ulcer trial registered a 0.5 mg/mL cream applied twice a week ^{[16] [18]}. The melanoma study started at 250 µg per tumour, injected every seven days for up to eight weeks ^[17]. No LL-37 dosage chart or daily protocol for injection has been tested in a published study, and the finding that the highest wound concentration worked no better than placebo is a reminder that more is not necessarily better ^[6].

Every human study of LL-37 applied it directly to a lesion: as a solution or cream on leg and foot ulcers ^{[6] [7] [16]}, or by injection into melanoma deposits ^{[8] [17]}. We found no published human study of LL-37 given by subcutaneous injection, by mouth or as a nasal spray. LL-37 is a relatively large peptide that the body releases from a precursor at sites of need ^[3], and there are no published data on how an injected dose is distributed or cleared in people.

Topical LL-37 on leg ulcers was well tolerated in both trials ^{[6] [7]}. Injected LL-37 is less well characterised: the melanoma case report describes significant skin toxicity after intratumoral injection ^[8], and laboratory and clinical research links excess LL-37 activity to psoriasis and rosacea ^{[4] [5]}.

The FDA has said that compounded drugs containing LL-37 may pose a risk of immune reactions (immunogenicity) for some routes of administration and of peptide-related impurities ^[10].

Because high LL-37 levels have been associated with the growth of some cancers, including ovarian, lung and breast cancer, as well as with suppression of others ^[9], the effect of long-term injected LL-37 on cancer risk is unknown. No study has examined it. Searches about LL-37 for bodybuilding or muscle have no evidence behind them either: we found no study of LL-37 and muscle, strength or body composition.

LL-37 is not approved as a medicine anywhere we are aware of. In the US, the FDA previously placed cathelicidin LL-37 in category 2 of its interim compounding policy, the list of bulk substances that may present significant safety risks; the nomination was later withdrawn and the FDA now lists it among substances previously in category 2 ^[10]. It was not among the peptides considered at the FDA’s July 2026 compounding advisory committee meeting. We have not confirmed its status on the WADA Prohibited List.

For rules on buying and holding research peptides in your country, see our legal status overview, including the UK page and the US page.

LL-37 is supplied as a freeze-dried powder. Peptides are generally stored cold, dry and away from light, and reconstituted solutions are refrigerated and used within a limited period. See how to store peptides and bacteriostatic water.

LL-37 is a relatively long peptide, which makes synthesis harder and purity testing more important. Compare prices, learn how to read a COA, and see our list of third-party tested suppliers.

We track LL-37 peptide listings in the UK and US. A certificate of analysis for LL-37 should report a measured mass close to its molecular weight of about 4493 g/mol, as a mass that does not match suggests a different or incomplete peptide. Our guides to third-party testing and spotting a fake supplier explain what else to check.