LL-37

LL-37 is the only human cathelicidin — a natural antimicrobial peptide the body makes as part of its immune system, best known for fighting microbes and supporting wound healing. Research shows it kills a broad range of bacteria and fungi, though it can also play a role in some inflammatory skin conditions like rosacea and psoriasis. It is not FDA-approved for any use and is sold only as a research peptide.

LL-37, a natural antimicrobial peptide, has been studied for fighting infection and wound healing. A strong preclinical base shows it kills a broad range of bacteria, fungi, and some viruses and plays a role in wound healing, and it is deficient in chronic wounds. There are no FDA-approved LL-37 drug products and the clinical evidence is limited. Research also shows LL-37 is "dual-edged": elevated levels are part of the inflammation seen in conditions like rosacea and psoriasis, so it is not simply anti-inflammatory.

Not FDA approved for any indication. Research-community use only. Available as a research peptide. Not listed in the WADA 2026 Prohibited List (the compound's mechanism is antimicrobial / immune-modulatory rather than performance-enhancing). Not-named is not not-prohibited: WADA's S0 (Non-Approved Substances) prohibits at all times any pharmacological substance "with no current approval by any governmental regulatory health authority for human therapeutic use (e.g. drugs under pre-clinical or clinical development)", which describes this compound — so S0 captures it by default and it is off-limits in drug-tested sport. Verified against the local archive `docs/legal/wada-2026-prohibited-list.txt` (S0 clause + full-text search returning no hit) on 2026-09-07. LL-37 is the only human cathelicidin — a single-gene product (CAMP gene) that represents the entire human cathelicidin family. Distinct from murine cathelicidin (mCRAMP) and from non-mammalian cathelicidins.

LL-37 is not FDA-approved, and its safety in humans has not been established in clinical trials. It is not named on the WADA Prohibited List, but it has no approval as a medicine anywhere, and WADA's S0 category prohibits exactly that by default, so treat it as off-limits in drug-tested sport. VialWise is a research and educational reference, not medical advice — consult a licensed professional.

⚠️ For research and educational purposes only. LL-37 is not approved by the FDA or any major Western regulatory agency as a pharmaceutical drug for any indication. Information in this entry is informational, not medical advice. Always confirm dose calculations and consult appropriate professional guidance before any protocol decisions.

⚠️ The only human cathelicidin — a load-bearing endogenous innate immunity peptide. Unlike most peptides covered elsewhere in this library (which are synthetic compounds with no direct human counterpart), LL-37 is endogenous to humans — it is the C-terminal 37-amino-acid active fragment of hCAP-18, the protein product of the human CAMP gene, and is the entirety of the human cathelicidin antimicrobial peptide repertoire.[¹] Free LL-37 is produced by neutrophils, macrophages, epithelial cells, and other tissues at sites of infection and inflammation, where it kills bacteria, fungi, and some viruses through membrane disruption and modulates downstream immune signaling. Researchers should be aware that exogenous LL-37 administration is supplementing a natively-expressed peptide rather than introducing a foreign biological — the safety implications of supraphysiologic exogenous exposure to an endogenous innate immunity peptide are different from those of a fully synthetic compound.

⚠️ The published clinical evidence base is limited. Despite a strong preclinical evidence base spanning antimicrobial activity, wound healing, and immune modulation,[¹][²] LL-37 has not produced FDA-approved drug products. Some topical LL-37 mimetics have entered clinical development for chronic wound indications, but no LL-37-specific approved indication exists as of this entry's last-updated date. Research-community use is supported by the strong preclinical mechanism literature plus the rationale that LL-37 is endogenous and therefore unlikely to produce qualitatively novel adverse effects at modest exogenous doses — but the clinical translation is not RCT-validated.

⚠️ Precision matters at low doses. LL-37 is dosed in micrograms per dose (typical research-community subcutaneous). At typical reconstitution concentrations the draws still land in the small-volume range on a U-100 syringe. Always verify draws against the in-app calculator and double-check the unit count on the syringe before injecting.

⚠️ LL-37 has dual-edged biological activity — pro-inflammatory and immunomodulatory in some contexts. While the dominant LL-37 framing is antimicrobial and wound-healing, the peptide also has pro-inflammatory and pro-angiogenic activities that contribute to its role in autoimmune and inflammatory conditions. Elevated LL-37 levels have been associated with rosacea, psoriasis, and atopic dermatitis pathophysiology — the peptide is part of the inflammatory cascade in these conditions. The review literature also links cathelicidins to cancer biology[¹] and, in dysregulated states, to neuroinflammation — one 2026 review describes LL-37 upregulation in brain tissue, binding to β-amyloid, and microglial cytokine release associated with Alzheimer's and Parkinson's pathology.[⁷] Researchers using exogenous LL-37 in inflammatory or autoimmune contexts should be aware that the peptide's role is not purely "anti-inflammatory" — it is a regulatory innate immunity peptide whose net effect depends on tissue context and concentration.

LL-37 is the C-terminal 37-amino-acid active fragment of human cathelicidin antimicrobial peptide-18 (hCAP-18), the protein product of the human CAMP (cathelicidin antimicrobial peptide) gene located on chromosome 3p21.[¹] The full-length hCAP-18 protein is enzymatically cleaved (predominantly by neutrophil-derived proteinase 3) at sites of inflammation, releasing the active LL-37 peptide. LL-37 is the only human cathelicidin — unlike many other species (cattle, pigs, mice) which express multiple cathelicidins, the human genome has a single CAMP gene producing a single mature antimicrobial peptide. This makes LL-37 a load-bearing component of the human innate immune system.

Mechanism — direct antimicrobial activity. LL-37 kills a broad spectrum of pathogens (Gram-positive bacteria, Gram-negative bacteria, mycobacteria, fungi, some enveloped viruses) primarily through membrane disruption.[¹][²] The amphipathic α-helical structure of the active peptide allows it to insert into and disrupt bacterial cell membranes — selective for bacterial membranes over mammalian membranes due to differences in lipid composition (negatively charged phosphatidylglycerol and lipopolysaccharide in bacteria vs neutral phosphatidylcholine in mammalian cells). LL-37 also has anti-biofilm activity and can disrupt established biofilms of clinically relevant pathogens including *Pseudomonas aeruginosa* and *Staphylococcus aureus*.[¹]

Mechanism — wound healing and re-epithelialization. Beyond direct antimicrobial activity, LL-37 plays a load-bearing role in wound healing. The peptide is strongly expressed in healing skin epithelium but is deficient in chronic ulcer epithelium — supporting a causal role in re-epithelialization.[²] Antibody-mediated neutralization of LL-37 inhibits wound closure in concentration-dependent fashion. Mechanisms include direct stimulation of keratinocyte migration, recruitment of inflammatory cells to the wound site, and pro-angiogenic effects that support neovascularization in granulation tissue. Adenovirus-mediated LL-37 gene transfer accelerates wound healing in diabetic ob/ob mice — demonstrating that exogenous LL-37 augmentation can rescue impaired healing.

Mechanism — immunomodulation and dual-edged activity. LL-37 has substantial activity beyond direct antimicrobial effects, modulating cytokine production, chemotactic activity, and adaptive immune responses.[⁶] The net effect is context-dependent — in acute infection LL-37 drives appropriate immune activation and pathogen clearance, but in chronic inflammatory conditions (rosacea, psoriasis, atopic dermatitis, some autoimmune contexts) elevated LL-37 levels contribute to pathological inflammation. Reviews of the cathelicidin class also describe roles in angiogenesis, apoptosis modulation, and cancer biology,[¹] and in neuroinflammation when the peptide is dysregulated.[⁷] Researchers using exogenous LL-37 in inflammatory contexts should be aware that the peptide is not purely "anti-inflammatory." As of this entry's last-updated date the cathelicidin immunotherapy literature remains preclinical — no pivotal exogenous-LL-37 human trial has read out.[⁶]

Common research interests. LL-37's research-community use spans: - Antimicrobial / antibiotic-resistant infection adjunct — research-community use for chronic infections, biofilm-associated infections, and antibiotic-resistant organism contexts on the rationale of mechanistically distinct microbial killing. - Wound healing (topical, including chronic wounds) — research-community use for slow-healing wounds, chronic ulcers, post-surgical recovery on the rationale of the strong preclinical wound-healing evidence base. - Skin conditions (acne, mild skin infections) — topical use for inflammatory acne and superficial bacterial skin infections. - Immune support / chronic infection contexts — research-community use for chronic Lyme disease, chronic viral infections, and immune dysregulation contexts. The clinical evidence for these uses is research-community-attributed rather than RCT-grade. - Anti-aging skin protocols — niche research-community use combining LL-37 with other anti-aging peptides; the evidence base for cosmetic anti-aging effects is essentially nonexistent.

Regulatory status. LL-37 is sold as a research peptide and has no FDA-approved indication. On 2026-04-22 the FDA removed cathelicidin (LL-37) from the Category 2 "Do Not Compound" interim list, as part of a batch of peptides whose original nominations were withdrawn.[⁵] A Pharmacy Compounding Advisory Committee (PCAC) review of LL-37 for the 503A Bulk Drug Substances List is scheduled before the end of February 2027, alongside GHK-cu, Melanotan II, Dihexa acetate, and PEG-MGF.[⁵] Removal from Category 2 does not, by itself, make LL-37 eligible for 503A compounding — LL-37 is not on the 503A bulks list, and its status is best described as reviewed-but-undecided pending that PCAC outcome. LL-37 is not listed in the WADA 2026 Prohibited List[⁴] — direct text-search of the canonical 2026 WADA pdf returned no matches. Not-named is not not-prohibited: WADA's S0 (Non-Approved Substances) prohibits at all times any pharmacological substance "with no current approval by any governmental regulatory health authority for human therapeutic use (e.g. drugs under pre-clinical or clinical development)", which describes this compound — so S0 captures it by default and it is off-limits in drug-tested sport. Verified against the local archive `docs/legal/wada-2026-prohibited-list.txt` (S0 clause + full-text search returning no hit) on 2026-09-07.

Commonly reported

• Injection site reactions (with subcutaneous use) — most common
• Mild flushing, warmth, or skin irritation (uncommon)
• Headache (uncommon, transient)
• No consistent pattern of serious adverse events in research-community reports
• Exacerbation of LL-37-driven chronic inflammatory conditions (psoriasis, rosacea, atopic dermatitis, some autoimmune contexts) — theoretical based on mechanism; researchers with these conditions should approach LL-37 with caution.
• Long-term safety in humans is essentially unknown. No multi-year human safety dataset exists for the modern research-community-use pattern.
• Effects on endogenous LL-37 production and innate immunity homeostasis — uncharacterized; the consequences of chronic exogenous LL-37 administration on endogenous CAMP gene expression are not known.
• Pregnancy and lactation safety — no data; default to contraindicated.

Active LL-37-driven chronic inflammatory conditions (psoriasis, rosacea, atopic dermatitis with elevated cathelicidin signal) — caution

Active autoimmune disease — caution; LL-37 has been implicated in autoimmune pathophysiology in some contexts

Pregnancy and lactation: no data; default to contraindicated

Pediatric use: no data — should not be used in researchers under 18

Known peptide allergy or hypersensitivity — contraindicated

Regulatory note (US): LL-37 is sold as a research peptide and is not on the FDA 503A bulks list. FDA removed cathelicidin (LL-37) from the Category 2 "Do Not Compound" interim list on 2026-04-22, and a PCAC review of LL-37 for the 503A bulks list is scheduled before the end of February 2027; that removal does not confer 503A-compounding eligibility and is not a safety or efficacy finding.[⁵]

Regulatory note (WADA): LL-37 is not listed in the 2026 WADA Prohibited List. Not-named is not not-prohibited: WADA's S0 (Non-Approved Substances) prohibits at all times any pharmacological substance "with no current approval by any governmental regulatory health authority for human therapeutic use (e.g. drugs under pre-clinical or clinical development)", which describes this compound — so S0 captures it by default and it is off-limits in drug-tested sport. Verified against the local archive `docs/legal/wada-2026-prohibited-list.txt` (S0 clause + full-text search returning no hit) on 2026-09-07.[⁴]

Peptide

A short chain of amino acids, the building blocks of proteins. Many compounds in this library are peptides.

Antimicrobial

able to kill or slow microbes such as bacteria and fungi.

Preclinical

Research done in cells or animals, before human clinical trials. Promising preclinical results don't always hold up in people.

Subcutaneous

An injection into the fatty layer just under the skin, rather than into a muscle or vein.

1. Vandamme D, Landuyt B, Luyten W, Schoofs L. (2012). A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cellular Immunology, 280(1):22-35. doi: 10.1016/j.cellimm.2012.11.009.(PMID 23246832)
2. Heilborn JD, Nilsson MF, Kratz G, Weber G, Sørensen O, Borregaard N, Ståhle-Bäckdahl M. (2003). The cathelicidin anti-microbial peptide LL-37 is involved in re-epithelialization of human skin wounds and is lacking in chronic ulcer epithelium. Journal of Investigative Dermatology, 120(3):379-89. doi: 10.1046/j.1523-1747.2003.12069.x.(PMID 12603850)
3. Duplantier AJ, van Hoek ML. (2013). The Human Cathelicidin Antimicrobial Peptide LL-37 as a Potential Treatment for Polymicrobial Infected Wounds. Frontiers in Immunology, 4:143. doi: 10.3389/fimmu.2013.00143.(PMID 23840194)
4. World Anti-Doping Agency. The 2026 Prohibited List, International Standard (effective 1 January 2026). Canonical PDF: wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf (local archival copy in `docs/legal/wada-2026-prohibited-list.pdf`). LL-37 is not listed in the 2026 WADA Prohibited List. S0 note (2026-09-07): not-named is confirmed, but this compound has no approval as a medicine anywhere, so WADA's S0 (Non-Approved Substances) captures it by default — the negative listing rules out a named prohibition, not prohibition.
5. US Food and Drug Administration — 503A bulk drug substances / Category 2 "Do Not Compound" interim list action of 2026-04-22, removing cathelicidin (LL-37) and 11 other peptides following withdrawal of the original nominations; a Pharmacy Compounding Advisory Committee (PCAC) review of LL-37 for the 503A Bulk Drug Substances List is scheduled before the end of February 2027 (with GHK-cu, Melanotan II, Dihexa acetate, and PEG-MGF). ⚠️ This item is sourced from regulatory/legal trade reporting, not peer-reviewed literature — reported by Frier Levitt ("FDA to Remove 12 Popular Peptides from the Category 2 'Do Not Compound' List," 2026), the FDA Law Blog ("FDA's Pep(tide) Rally!," April 2026), and The Peptide Catalog ("12 Peptides Off FDA Category 2: April 22 2026").
6. Ding A, Lu Z, Wu J, et al. (2026). Cathelicidin antimicrobial peptides: current progress and future prospects in immunotherapy. Developmental & Comparative Immunology, 180:105642 (2026 Jun 1). doi: 10.1016/j.dci.2026.105642.(PMID 42229867)
7. Asti AL. (2026). β-Amyloid (Aβ) and Human Cathelicidin LL-37: Two Sides of the Same Coin? International Journal of Molecular Sciences, 27(12):5460 (2026 Jun 17). doi: 10.3390/ijms27125460.(PMID 42353177)

• BPC-157 / TB-500 Blend — discussed together in this entry's stacks section
• Thymosin Alpha-1 — discussed together in this entry's stacks section
• VIP — same mechanism class
• ARA-290 — shared research area
• BPC-157 — shared research area
• Chonluten — shared research area