The Sunlight Experiment

Supplement Monograph

LL-37

PeptideImmune

LL-37 is the only human cathelicidin antimicrobial peptide, a component of innate immunity studied for antimicrobial and wound-healing effects; not an approved supplement.

Work in progress Updated July 2026

What Is LL-37?

LL-37 is the only human member of the cathelicidin family of antimicrobial peptides — a 37-residue host-defence peptide cleaved from the precursor hCAP18 and produced by neutrophils, epithelial and other cells. It has broad-spectrum antimicrobial activity and also acts as an immune modulator, and is of interest for antimicrobial, immune and wound-healing applications. As a supplement/injectable “research peptide” it is not approved; the science is mostly basic immunology plus some topical wound trials.

Evidence

LL-37 directly disrupts microbial membranes and modulates immune-cell recruitment, biofilm formation and wound closure; its biology as the sole human cathelicidin is summarised in a widely cited review 1Reference 1Dürr UHN et al. · 2006ReviewLL-37, the only human member of the cathelicidin family of antimicrobial peptides — reviewView study →. Topically, an early randomised placebo-controlled trial reported enhanced healing of hard-to-heal venous leg ulcers with LL-37 2Reference 2Grönberg A et al et al. · 2014RCTTreatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial — randomised/RCTView study →, but a later phase-2b randomised trial found no significant benefit in the overall population (with a signal only in a large-ulcer subgroup) 3Reference 3Mahlapuu M et al et al. · 2021RCTEvaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial — randomised/RCTView study → — so wound-healing efficacy in humans is mixed and unconfirmed. Systemic “immune-boosting” claims for injected LL-37 are marketed but I found no human trial supporting them in this pass.

Dosage & Safety

There is no established supplement dose; human dosing data are limited to topical wound-trial concentrations and are not a personal recommendation. LL-37 is not an approved dietary supplement or drug; systemic/injectable safety, interactions, pregnancy safety and long-term effects are not established. Note LL-37 has context-dependent biology (it can be pro-inflammatory and has been implicated in some autoimmune conditions), which is a further reason systemic self-use is uncharacterised. Informational only.

References

  1. Dürr UHN, Sudheendra US, Ramamoorthy A (2006). LL-37, the only human member of the cathelicidin family of antimicrobial peptides — review. Biochim Biophys Acta. https://pubmed.ncbi.nlm.nih.gov/16716248/
  2. Grönberg A et al. (2014). Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial — randomised/RCT. Wound Repair Regen. https://pubmed.ncbi.nlm.nih.gov/25041740/
  3. Mahlapuu M et al. (2021). Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial — randomised/RCT. Wound Repair Regen. https://pubmed.ncbi.nlm.nih.gov/34687253/