Cite this answer
LL-37: quick citable summary
LL-37 is listed by PeptaHub as a immune peptide with a reclassification pending legal-status classification. The page summarizes mechanism, research context, common routes, safety notes, and references for writers and AI answer engines.
PeptaHub. “LL-37: Mechanism, Research Context, Safety.” peptahub.com, 2026. https://peptahub.com/peptides/ll-37. Licensed CC BY 4.0.
License: Creative Commons Attribution 4.0 International. Link back to https://peptahub.com/peptides/ll-37.
What is LL-37?
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid fragment of hCAP-18 with broad-spectrum activity against bacteria, viruses, and fungi. Its human evidence is a single 34-patient trial of topical LL-37 on venous leg ulcers; injected use is untested.
Overview
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino-acid peptide cleaved from the precursor protein hCAP-18. It is produced by immune cells (neutrophils, macrophages), epithelial cells, and keratinocytes as part of the innate immune response. It has broad-spectrum antimicrobial activity against bacteria, viruses, and fungi, and plays a role in wound healing and immune modulation.
Mechanism of action
LL-37 has a helical amphipathic structure that allows it to insert into and disrupt microbial cell membranes, creating pores and causing lysis. Beyond direct antimicrobial action, it modulates the immune response by recruiting immune cells (chemotaxis), promoting wound healing, inhibiting biofilm formation, neutralizing bacterial endotoxins (LPS), and modulating TLR signaling. Vitamin D regulates LL-37 expression, linking vitamin D deficiency to increased infection susceptibility.
Reported study ranges
| Purpose | Route | Reported range | Frequency | Notes |
|---|---|---|---|---|
| immune support | subcutaneous | 50–100 mcg | daily | Community-reported range for systemic immune support, with no trial behind it. The one controlled human study of LL-37 used topical application to leg ulcers, not subcutaneous injection, so it does not support this route, indication, or dose. |
Reported ranges are for research context only. Consult a qualified healthcare professional before using any peptide.
Convert LL-37 research-range units
Need to convert mg to mcg, dose volume, or U-100 syringe units? The LL-37 dose calculator is preloaded with these ranges, or use the general dose unit converter.
Research summary
Extensive research on innate immunity. Studies show broad-spectrum activity against MRSA, E. coli, Pseudomonas, Candida, and enveloped viruses including influenza and HIV. Anti-biofilm activity demonstrated against surgical implant infections. One first-in-man randomized placebo-controlled trial in 34 patients with hard-to-heal venous leg ulcers found topical LL-37 at 0.5 and 1.6 mg/mL improved healing-rate constants versus placebo and was well tolerated, with no benefit at the highest 3.2 mg/mL dose (Grönberg, Wound Repair Regen 2014). That is the only controlled human efficacy trial. Vitamin D upregulates cathelicidin gene expression, which is the proposed mechanistic link between vitamin D status and innate immune defence.[1][2][3][4][5][6]
Evidence grading
Each claimed benefit is graded by the strength of available evidence. Grades reflect study quality, not effect size.
Strong = multiple RCTs · Moderate = limited trials or observational · Preliminary = animal or in vitro only · Insufficient = anecdotal or no published data
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
Common stacks
Peptides commonly paired with LL-37 for synergistic effects.
Legal status
LL-37 cannot legally be compounded in the US today. It is one of 12 peptides the FDA removed from Category 2 of the interim 503A bulk drug substances list on April 15, 2026, effective within seven calendar days, because the original nominators withdrew their nominations. Removal from Category 2 is not the same as being added to the Section 503A Bulks List or placed in Category 1, and the FDA has been explicit that it does not by itself make a substance eligible for compounding — enforcement discretion extends only to Category 1, and these substances were never in Category 1. LL-37, which the FDA lists as cathelicidin, was not among the seven peptides heard on July 23-24, 2026; the FDA has stated the Pharmacy Compounding Advisory Committee will reconvene before the end of February 2027 to consider it alongside GHK-Cu, dihexa acetate, Melanotan II, and PEG-MGF. PCAC is advisory and formal rulemaking afterward typically takes 12 to 24 months, so compounding status is unlikely to change quickly. LL-37 is not FDA-approved for any indication and is otherwise sold as a research peptide; it remains in clinical development for wound healing and infection applications. Verify current federal and state rules before relying on access claims.
Sourcing & access
Reclassification in progress
LL-37is one of 12 peptides the FDA removed from its Category 2 “do not compound” list on April 15, 2026, after the original nominations were withdrawn. That removal did not place it on the 503A Bulks List or into Category 1, so it is not currently eligible for compounding. The Pharmacy Compounding Advisory Committee is reviewing these substances for the Bulks List; adding one requires formal rulemaking, which typically takes 12 to 24 months. See our regulatory status tracker and regulatory timeline for the current position.
Frequently asked questions
LL-37 is a 37-amino acid antimicrobial peptide cleaved from the precursor protein hCAP-18. It is produced by immune cells and epithelial cells as part of the innate immune response and has broad-spectrum activity against bacteria (including MRSA), viruses, and fungi.
LL-37 has an amphipathic helical structure that inserts into and disrupts microbial cell membranes. Beyond direct antimicrobial action, it recruits immune cells, promotes wound healing through angiogenesis, inhibits biofilm formation, and neutralizes bacterial endotoxins.
Reported side effects include injection site reactions, redness or swelling, and rare mild fever attributed to immune activation. LL-37 is not FDA-approved and is available only as a research peptide. The human safety data come from a single 34-patient topical wound-healing trial, in which no local or systemic safety concerns were reported. Long-term and systemic safety in humans is not characterized.
Vitamin D regulates LL-37 gene expression through the vitamin D receptor, which binds a response element in the cathelicidin gene. This pathway is the proposed mechanism linking vitamin D deficiency to greater susceptibility to infection. Whether raising LL-37 through supplementation reduces infections in practice has not been settled by trials.
Research references
- LL-37, the only human member of the cathelicidin family of antimicrobial peptidesPubMed
- Cathelicidin LL-37: a multitask antimicrobial peptideReview
- Therapeutic Potential of Cathelicidin Peptide LL-37, an Antimicrobial Agent, in a Murine Sepsis ModelPubMed
- The Human Cathelicidin Antimicrobial Peptide LL-37 and Mimics are Potential Anticancer DrugsPubMed
- Antimicrobial peptide LL-37 promotes bacterial phagocytosis by human macrophagesPubMed
- Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trialPubMed