LL-37

Definition

LL-37 is the only cathelicidin-derived antimicrobial peptide found in humans, cleaved from the precursor protein hCAP18. It is produced by neutrophils and by epithelial cells at barrier surfaces, and its expression is induced by vitamin D, which is why so much of its literature is a vitamin D literature ^[1].

Its functions extend past direct antimicrobial killing to chemotaxis, wound repair, and modulation of inflammation ^[2]. That breadth is the reason it is marketed, and also the reason its record is easy to misread: a peptide the body already makes accumulates studies about the body making it.

Evidence

The distinction that governs this page is between a study of the peptide and a study of the person's own peptide. Across five name variants, PubMed returns 3,076 indexed records, of which 2,199 carry the Humans subject heading, 72 the clinical-trial publication type, and 45 the randomized-controlled-trial type ^[3].

All seventy-two trial-type records were opened and read rather than counted, and sixty-eight of them do not administer LL-37 to anyone. They measure a participant's own cathelicidin concentration after vitamin D supplementation, after exercise, after a probiotic, or as a biomarker in tuberculosis, cystic fibrosis, chronic obstructive pulmonary disease, sepsis, and periprosthetic joint infection ^[3]. Reported as a trial count for the compound, seventy-two would have been a false number by a factor of eighteen.

Four records administer the peptide. Three are wound-healing studies: two randomized placebo-controlled trials of LL-37 in hard-to-heal venous leg ulcers, published in 2014 and 2021, and a 2023 randomized trial of an LL-37 cream in diabetic foot ulcer ^[3]. The fourth is a 2023 randomized trial of an oral preparation against a SARS-CoV-2 variant ^[3]. All four are topical or oral. None is an injectable study, and injection is the route the compound is sold for.

Lawful access

There is no lawful United States supply route. Cathelicidin LL-37 sat in Category 2 of FDA's interim section 503A bulks list and left it in April 2026 when the nomination was withdrawn by its nominators. It was not added to Category 1, and it appears in no category of the list FDA published on May 14, 2026 ^[4].

FDA's safety finding survives the withdrawal and is unusually specific. The agency states that it lacks sufficient safety-related information regarding cathelicidin LL-37 to know whether the drug would cause harm when administered to humans, and that nonclinical research findings suggest detrimental effects on male reproduction and that the drug can be pro-tumorigenic in some tissues ^[5]. Most entries in that table record an absence of information; this one records an absence of information alongside two directional signals of harm.

Enforcement history exists as well. In April 2020 FDA warned a compounding pharmacy that products it compounded using LL-37 and twenty-one other substances were not eligible for the exemptions in section 503A(a), and stated in the same letter that those substances had not been nominated for inclusion on the 503A bulks list ^[6]. Material sold under this name is research-use-only chemical supply; the research-only page explains what that posture does and does not mean.

Related molecules

The index files LL-37 with the immune peptides beside thymosin alpha-1, which reached an advisory committee and was refused while this molecule never reached one at all. The human trial record prints the seventy-two against every other count in the index, and what removal does not mean covers the cohort this molecule left Category 2 with.

Elsewhere in this index