LL-37

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.

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].

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].

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].

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.

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].

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.

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.