LL-37 is a peptide your own body makes. It is the only member of the cathelicidin family found in humans, and it is named for its first two amino acids: two leucines at the start of a 37-residue chain (Frontiers in Immunology, 2013). The peptide is stored as part of a larger precursor protein, hCAP18 (also written CAP18), and is released when enzymes cut the active 37-amino-acid fragment from the precursor's tail.
That origin explains the synonyms you will see on labels: CAP-18, hCAP18/LL-37, "cathelicidin antimicrobial peptide LL-37." The synthetic drug-development version has been given the name ropocamptide.
What it does
LL-37 has two jobs that researchers tend to talk about separately.
The first is direct killing of microbes. Residues 13 to 34 fold into an amphipathic helix that inserts into microbial membranes, and the peptide is active against both Gram-negative and Gram-positive bacteria, including drug-resistant strains (Biochimica et Biophysica Acta, 2015). It also interferes with biofilm formation at concentrations well below those needed to kill bacteria outright, and it can bind and neutralize bacterial lipopolysaccharide (Frontiers in Immunology, 2013).
The second is signaling. LL-37 acts as an alarmin, recruiting immune cells, modulating inflammation, and pushing keratinocytes and fibroblasts to migrate and proliferate, which is why it keeps coming up in wound-healing work. Its effects are concentration-dependent. Low amounts support cell survival and repair; higher amounts turn cytotoxic.
State of the human research
Unlike most peptides sold to researchers, LL-37 has actually been into the clinic, in two very different settings.
Chronic wounds. The Swedish company Promore Pharma developed the synthetic version, ropocamptide, as a topical treatment for venous leg ulcers. Its Phase IIb "HEAL LL-37" trial enrolled 144 patients across two doses (0.5 and 1.6 mg/ml) plus placebo, applied twice weekly with compression therapy over roughly 13 weeks. The headline result was mixed but real: the whole-group difference was not statistically significant, but patients with larger ulcers (10 cm² and above) showed a significant improvement versus placebo, with the lower dose performing better (Promore Pharma). The results were published in Wound Repair and Regeneration.
Melanoma. A separate Phase I trial gave LL-37 as weekly injections directly into cutaneous melanoma metastases (ClinicalTrials.gov NCT02225366), on the theory that it activates plasmacytoid dendritic cells inside the tumor. A case report in the Journal of Cutaneous Pathology documented one patient who developed multiple skin lesions about 45 days in, with keratoacanthoma-like features on biopsy. The lesions resolved within two months of stopping injections (J Cutan Pathol, 2018).
Neither use is approved. LL-37 is not an FDA- or EMA-cleared drug, and ropocamptide remains investigational.
One caution worth flagging: LL-37 is not uniformly "good." In melanoma biology, some studies suggest it can also promote local tumor invasion, which is a reminder that this is a context-dependent molecule, not a simple therapeutic.
Status and what buyers see
Material sold under the LL-37 name is offered strictly for research use only. It is not approved for human consumption, and nothing here is medical, dosing, or efficacy advice. LL-37 is an endogenous human peptide rather than a classic performance-enhancing drug, so it is not on the typical anabolic or growth-hormone lists, but anyone subject to anti-doping rules should confirm current status with their own governing body rather than assume.
Because LL-37 is a 37-residue peptide, identity and purity are the practical concerns for anyone evaluating a vial. The questions that matter are whether the listed sequence and mass match, what purity a third-party assay (typically HPLC) reports, and whether a batch-specific Certificate of Analysis is available. peptideone aggregates published vendor COAs and independent purity ratings so those claims can be compared rather than taken on faith.
Facts above are attributed to the cited sources. peptideone sells nothing, runs no tests of its own, and offers no medical advice.