LL-37

What it is

LL-37 is the active peptide generated from the human cathelicidin antimicrobial protein hCAP18^{[6 ]}. It is part of the innate immune system and is expressed by epithelial cells and immune cells at barrier surfaces. Bals and colleagues reported LL-37/hCAP18 expression in human airway epithelium and broad antimicrobial activity at the airway surface^{[6 ]}.

LL-37 is not simply a natural antibiotic. It can also influence wound repair, keratinocyte migration, immune-cell signaling, angiogenesis, and inflammatory pathways^{[7 –13 ]}. Tokumaru and colleagues reported that LL-37 induced keratinocyte migration through transactivation of the epidermal growth factor receptor, providing one mechanistic basis for wound-healing research^{[7 ]}.

Because LL-37 is involved in immune defense and tissue repair, it has been studied as a topical or local wound-healing candidate. Randomized clinical trials have evaluated LL-37 in hard-to-heal venous leg ulcers and diabetic foot ulcers^{[8 –10 ]}. These trials are clinically relevant, but LL-37 has not become an FDA-approved wound product in the United States.

LL-37 also has context-dependent risk biology. It has been implicated in psoriasis pathogenesis through complexes with self-DNA and self-RNA that activate dendritic-cell pathways^{[12 –14 ]}. It has also been studied in cancer biology, including breast-cancer expression and growth-factor-like effects in epithelial cells^{[11 ]}. Those findings help explain why “immune peptide” claims must be presented cautiously.

Regulatory status

LL-37 is not FDA-approved in the United States for infection prevention, wound healing, diabetic foot ulcers, venous leg ulcers, immune support, Lyme disease, biofilm treatment, dermatology, or any other indication. No FDA-approved LL-37 prescribing label was identified for this draft.

503A — withdrawn nomination, future PCAC consultation

For 503A compounding, FDA states that bulk substances must meet a USP/NF monograph pathway, be components of FDA-approved drug products when no monograph exists, or appear on FDA’s 503A bulks list^{[1 ]}. LL-37 is not on the current 503A bulks list. FDA’s April 22, 2026 category document states that “Cathelicidin LL-37” was removed from Category 2 because the nomination was withdrawn, but FDA intends to consult PCAC before the end of February 2027 regarding potential inclusion on the 503A bulks list^{[2 ]}.

FDA safety concerns

FDA’s significant-safety-risk page states that compounded drugs containing cathelicidin LL-37 may pose immunogenicity risk for certain routes and peptide-related impurity/API-characterization concerns^{[4 ]}. FDA also states that it lacks sufficient safety-related information to know whether the drug would cause harm when administered to humans and notes nonclinical findings suggesting detrimental effects on male reproduction and protumorigenic effects in some tissues^{[4 ]}.

503B and controlled-substance status

For 503B outsourcing facilities, FDA states that bulk drug substances must appear on the 503B bulks list or be used for a drug on the FDA shortage list at the time of compounding, distribution, and dispensing^{[3 ]}. No 503B pathway for LL-37 was identified. LL-37 is not listed in 21 CFR Part 1308 as reviewed on May 7, 2026^{[5 ]}.

Date of last regulatory verification: May 7, 2026.

Research summary

Foundational work established LL-37 as an endogenous antimicrobial peptide. Bals and colleagues identified LL-37/hCAP18 expression in human lung epithelium and described broad antimicrobial activity at the airway surface^{[6 ]}. This helped establish LL-37 as part of innate epithelial defense, but endogenous expression is not the same as proof that administered LL-37 is safe or effective.

Wound-healing clinical trials

Wound-healing research is the strongest human clinical area. Gronberg and colleagues conducted a randomized, placebo-controlled trial in hard-to-heal venous leg ulcers and reported that LL-37 treatment enhanced healing^{[8 ]}. Mahlapuu and colleagues later conducted a multicenter prospective randomized placebo-controlled trial in hard-to-heal venous leg ulcers^{[9 ]}. Miranda and colleagues reported a randomized double-blind controlled trial of LL-37 cream in diabetic foot ulcers^{[10 ]}. These studies support continued drug-development interest but have not resulted in US FDA approval as of May 7, 2026.

Mechanistic wound data include keratinocyte migration. Tokumaru and colleagues reported that LL-37 induced keratinocyte migration through EGFR transactivation^{[7 ]}. This supports biological plausibility for wound repair but also underscores that LL-37 can influence growth and signaling pathways beyond antimicrobial killing.

Psoriasis and autoimmune concerns

Psoriasis and autoimmune inflammation are important counterweights to promotional claims. Lande and colleagues reported that plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide, a mechanism relevant to psoriasis^{[12 ]}. Ganguly and colleagues later described self-RNA-antimicrobial peptide complexes activating dendritic cells through TLR7 and TLR8^{[13 ]}. Reviews have discussed LL-37 as a defense molecule with potential pathogenic roles in psoriasis^{[14 ]}.

Cancer biology

Cancer biology is also context-dependent. Heilborn and colleagues reported high hCAP18/LL-37 expression in breast cancer and described it as a putative growth factor for epithelial cells^{[11 ]}. FDA’s safety-risk page similarly notes nonclinical protumorigenic findings in some tissues^{[4 ]}. These data do not prove that LL-37 causes cancer in humans, but they are incompatible with blanket claims that LL-37 is a generally safe immune-support peptide.

Route-specific interpretation

The wound-trial evidence also needs route-specific interpretation. The venous leg ulcer and diabetic foot ulcer trials evaluated local or topical wound-directed products in defined wound-care settings^{[8 –10 ]}. They do not establish that compounded injectable LL-37 treats systemic infection, improves immune defense, clears biofilms in vivo, or benefits people without chronic wounds.

The strongest mechanistic lesson is context dependence. LL-37 can support epithelial repair biology in one setting^{[7 ]}, participate in antimicrobial defense in another^{[6 ]}, and contribute to autoimmune skin inflammation when complexed with self nucleic acids^{[12 –14 ]}. An editorial page should therefore avoid describing LL-37 as simply “pro-healing” or “immune boosting.”

For evidence grading, LL-37 sits between early research peptides and approved drugs. It has randomized human wound studies^{[8 –10 ]}, but it also has unresolved regulatory, manufacturing, route, immune, reproductive, and cancer-biology questions^{[2 ,4 ,11 –14 ]}. Both sides belong in the page.

Public discourse

No qualifying public-discourse entries were identified for this page. Search results identified research papers, company or clinic pages, and anonymous forum discussion, but no accessible named-source podcast, article, or transcript with a verifiable quote meeting this site’s citation standard.

Public discourse reflects the views of the speakers cited and does not represent medical advice or the editorial position of ProPeptideGuide.

Side effects and safety

Clinical wound studies provide some local safety information, but they do not establish systemic or long-term safety for unapproved LL-37 products^{[8 –10 ]}. Local wound and skin reactions are the most relevant concerns in topical or local wound contexts, while injection or systemic use raises different unanswered questions.

FDA’s broader concerns

FDA’s concerns are broader than reported wound-trial tolerability. FDA cites potential immunogenicity, peptide-related impurities, API-characterization challenges, inadequate safety information, nonclinical male-reproductive concerns, and protumorigenic effects in some tissues^{[4 ]}. These concerns are especially important for compounded or grey-market injectables.

Mechanism-based concerns

Mechanistically, LL-37 can promote inflammatory recognition of self nucleic acids in psoriasis-related pathways^{[12 –14 ]}. That does not mean LL-37 will cause psoriasis in every context, but it does mean immune activation is not uniformly beneficial.

Long-term safety unknown

No FDA-approved label exists for LL-37, so there is no official contraindication list, drug-interaction section, pregnancy/lactation safety information, or long-term postmarketing surveillance. Patients with active malignancy, autoimmune disease, chronic wounds, diabetic foot disease, or infection are medically complex populations in which unapproved products create added risk.

The FDA-noted male-reproductive and protumorigenic concerns should be handled carefully^{[4 ]}. They do not prove that every LL-37 exposure causes reproductive harm or cancer. They do mean that broad safety claims would be inappropriate and that long-term, systemic, or repeated exposure should not be implied safe from short wound studies.

Available through

LL-37 is not currently available through FDA-compliant prescription or compounding channels in the United States as of 2026-05-07^{[1 –4 ]}. ProPeptideGuide does not link to or endorse grey-market vendors.