LL-37

LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino-acid endogenous peptide derived from the hCAP18 precursor with broad-spectrum activity against bacteria, viruses, and fungi, plus extensive immunomodulatory effects on host cells. It is the most clinically-developed cathelicidin peptide and the focus of substantial research interest in antimicrobial resistance and immune dysregulation contexts. Important regulatory update: LL-37 was removed from the FDA's Category 2 bulk substances list on April 22, 2026 and is scheduled for PCAC review before the end of February 2027.

Sources: FDA 503A bulk drug substances (Category 1/2) page; FDA Pharmacy Compounding Advisory Committee meeting scheduled before end of February 2027 — 503A bulks consideration (LL-37, dihexa acetate, injectable GHK-Cu, PEG-MGF, melanotan II), FDA

What is LL-37 and how does the cathelicidin antimicrobial mechanism work?

LL-37 is the active form of the human cathelicidin antimicrobial peptide, cleaved from the hCAP18 precursor and expressed by neutrophils, epithelial cells, and other immune-relevant cell populations. It has multiple mechanisms: direct antimicrobial activity through membrane disruption of bacteria, viruses (including respiratory pathogens), and fungi; immune-modulatory effects including chemotactic signaling and inflammation regulation; and tissue-repair effects through epithelial cell migration and wound healing pathways.

Evidence level: preclinical extensive (antimicrobial, immune, wound healing); limited human clinical trials

What does the research show for LL-37?

Preclinical studies have demonstrated broad antimicrobial activity, including against multidrug-resistant bacteria, immune-modulatory effects in chronic inflammatory conditions, and wound-healing acceleration in various injury models. Beyond direct antimicrobial action, LL-37 is a potent immunomodulator with a double-edged role: it can bind extracellular self-DNA and convert it into a strong trigger of type-I interferon production by plasmacytoid dendritic cells — a mechanism implicated in the autoimmune skin disease psoriasis and studied in lupus. Human clinical research has explored LL-37 derivatives in topical wound care, anti-inflammatory contexts, and antimicrobial applications. The native LL-37 sequence has been studied less in formal Phase 2/3 trials than engineered derivatives.

Source: Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide, Lande R., Gregorio J., Facchinetti V., Chatterjee B., Wang Y.-H., Homey B., et al., Nature, 2007 · Evidence level: preclinical extensive; human clinical for derivatives more than native LL-37

How does LL-37 compare to other antimicrobial and immune peptides?

LL-37 is the human-genome-encoded antimicrobial peptide — distinguishing it from synthetic antimicrobial peptides developed as therapeutic candidates and from other immune-modulating compounds.

What are the documented side effects of LL-37?

LL-37 administration can produce mild injection-site reactions and, at higher doses, mast cell degranulation effects (transient histamine-mediated symptoms). As an endogenous peptide, LL-37 has favorable inherent safety, but high-dose administration may produce dose-related inflammatory effects through its own immune-modulatory mechanism. Long-term safety at sustained research-use dosing is not well-characterized in human RCT.

Evidence level: preclinical safety; human safety from derivatives studies; long-term unestablished

What is the regulatory status of LL-37?

LL-37 is not approved for any medical indication anywhere in the world as of August 2026. It was one of 12 peptides the FDA removed from its Category 2 "may present significant safety risks" bulk-substances list in April 2026 (the FDA's list was updated April 22, 2026); the FDA now lists cathelicidin LL-37 among bulk substances "nominated but withdrawn." Removal from Category 2 does not authorize compounding-pharmacy production — LL-37 has not been added to Category 1 or the 503A bulk drug substances list, leaving it in a regulatory gray area. The FDA has scheduled LL-37 for Pharmacy Compounding Advisory Committee (PCAC) consideration for the 503A bulks list before the end of February 2027, alongside dihexa acetate, injectable GHK-Cu, PEG-MGF, and melanotan II; that determination is still pending. Current status in FDA peptide regulation 2025–2026 timeline.

Sources: FDA 503A bulk drug substances (Category 1/2) page; FDA Pharmacy Compounding Advisory Committee meeting scheduled before end of February 2027 — 503A bulks consideration (LL-37, dihexa acetate, injectable GHK-Cu, PEG-MGF, melanotan II), FDA

Why does LL-37 vendor verification matter?

LL-37's 37-amino-acid length makes synthesis quality control more variable than for shorter peptides, and the cationic amphipathic structure can lead to misfolding or aggregation issues that affect activity. Independent HPLC purity testing and mass spectrometry identity confirmation are essential. Endotoxin testing is particularly important given the immune-modulatory mechanism. Guidance in how-to-test-peptides hub.

How does Peptigrity verify LL-37 vendors?

Peptigrity collects independent third-party Certificates of Analysis for LL-37 from shops' official channels and verifies each for authenticity before publishing. Because shops choose which COAs to publish, results reflect the batches shops have made public rather than every production batch — a selection bias we state openly. A community-funded Testing Grant to purchase and test vials anonymously is in development. For a 37-residue cationic peptide, HPLC purity, mass-spectrometry identity confirmation, and endotoxin testing are the checks that matter most. Tests in the database come from independent labs such as Janoshik Analytical, Freedom Diagnostics, and Chromate.

Frequently asked questions

What does LL-37 do?

LL-37 is the only human cathelicidin antimicrobial peptide, with broad-spectrum activity against bacteria, viruses, and fungi, plus extensive immune-modulatory and wound-healing effects. Preclinical evidence is substantial; human clinical evidence is more developed for engineered derivatives than for native LL-37.

Is LL-37 legal to purchase?

LL-37 is legal to purchase as a research chemical for laboratory use in most jurisdictions, but it is not approved for human consumption. The April 22, 2026 Category 2 removal opens a potential future compounding pathway pending PCAC review before the end of February 2027. Country breakdown in peptide legal status guide.

When will the FDA decide on LL-37?

LL-37 is scheduled for Pharmacy Compounding Advisory Committee (PCAC) review before the end of February 2027 (alongside dihexa acetate, injectable GHK-Cu, PEG-MGF, and melanotan II). Removal from Category 2 in April 2026 was a procedural step; formal authorization for compounding pharmacy production remains pending PCAC determination. Track developments in FDA peptide regulation 2025–2026 timeline.

Source: FDA Pharmacy Compounding Advisory Committee meeting scheduled before end of February 2027 — 503A bulks consideration (LL-37, dihexa acetate, injectable GHK-Cu, PEG-MGF, melanotan II), FDA

Is LL-37 effective against antibiotic-resistant bacteria?

Preclinical evidence has demonstrated LL-37 activity against multidrug-resistant bacteria including MRSA and other antibiotic-resistant pathogens, with the membrane-disruption mechanism less prone to traditional resistance pathways. Human clinical evidence for antimicrobial resistance applications is more limited.

How can I verify an LL-37 vendor is selling real product?

Independent third-party HPLC certificate of analysis from a lab the vendor does not own or pay, with mass spectrometry identity confirmation and endotoxin testing. The 37-amino-acid length makes purity verification more important than for shorter peptides. COA interpretation in red flags in peptide certificates of analysis.

Does Peptigrity recommend an LL-37 dose?

No. LL-37 is not approved for human consumption and Peptigrity is an independent review platform, not a medical authority. Research-use dosing varies widely. Anyone considering use should consult a licensed physician.

This section is for educational and informational purposes only and does not constitute medical advice. LL-37 is not approved by the FDA or any major Western regulator for human use, though it was removed from Category 2 of the FDA 503A bulk substances list in April 2026 and is scheduled for PCAC review in early 2027. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.