LL-37

Areas of active research — not promised effects

Each tag links to other compounds with research into that goal. Research use only: these are areas of study, not human-use claims.

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LL-37 has no FDA-approved New Drug Application. It was originally placed on the FDA Section 503A Category 2 bulk drug substances list, which restricts use in pharmaceutical compounding. On April 15, 2026, FDA formally removed LL-37 from Category 2 as part of an HHS-directed action covering 12 peptides. However, removal from Category 2 does not constitute approval for 503A compounding; it means the substance has exited the 'do not compound' list pending formal PCAC evaluation. LL-37 is scheduled for PCAC review before the end of February 2027 (not included on the July 23–24, 2026 PCAC agenda). Until a favorable PCAC vote and formal listing on the 503A Bulks List, compounding of LL-37 at 503A and 503B pharmacies remains unauthorized. It is available as an RUO reagent from licensed research suppliers.

Transparent blend · bci-1.0 · never paid-placement

Primary name

LL-37

Origin

LL-37 is the sole human cathelicidin, generated by proteolytic cleavage of the C-terminal domain of the precursor protein hCAP18 (human cationic antimicrobial protein 18, encoded by the CAMP gene). Cleavage is performed primarily by serine proteases — including kallikreins in skin and proteinase 3 in neutrophils — releasing the 37-residue amphipathic alpha-helical peptide. The name reflects its two N-terminal leucine residues and its 37-amino-acid length. hCAP18/LL-37 is constitutively expressed in neutrophils and epithelial cells (skin, gut, lung, reproductive tract) and is induced by infection, inflammation, and vitamin D signaling.

Registry IDs

PubChem CID

16198951

CAS

154947-66-7

InChIKey

POIUWJQBRNEFGX-XAMSXPGMSA-N

ChEMBL

CHEMBL530345

Molecular formula

C205H340N60O53

Molar mass

4493 g/mol

Monoisotopic

4490.5754259 Da

InChIKey

POIUWJQBRNEFGX-XAMSXPGMSA-N

Appearance

White to off-white lyophilized powder

Solubility

Soluble in water and dilute aqueous buffers; solubility improved in dilute aceti…

Sequence not available in current seed.

Stability: LL-37 is susceptible to proteolytic degradation in biological fluids due to serine proteases and matrix metalloproteinases; stability in serum is limited (minut

Vial sizes

1 mg · 5 mg

Purity grades

≥95% HPLC / ≥98% HPLC

Salt forms

Free base (primary)

• GHS hazard class on file
• PPE & spill response
• Disposal guidance
• Not-for-human-consumption posture

How much research exists, and of what maturity — never a verdict on whether it works.

Mechanism of action

• LL-37 exerts antimicrobial activity primarily through electrostatic attraction to anionic bacterial membranes followed by adoption of an amphipathic alpha-helical conformation that intercalates into and disrupts the lipid bilayer, causing depolarization, pore formation, and membrane lysis; this mechanism extends to Gram-positive and Gram-negative bacteria, fungi, and enveloped viruses
• Independently of direct membrane disruption, LL-37 acts as an immunomodulator: it engages formyl peptide receptor 2 (FPR2/FPRL1) and the purinergic receptor P2X7 on immune cells to drive chemotaxis of neutrophils, monocytes, and T-cells to sites of infection, and it binds and neutralizes lipopolysaccharide (LPS) and lipoteichoic acid, blunting septic inflammatory cascades
• At higher concentrations LL-37 also transactivates the epidermal growth factor receptor (EGFR) and promotes keratinocyte migration, angiogenesis, and wound re-epithelialization
• The balance between pro- and anti-inflammatory outputs is concentration- and microenvironment-dependent

Pharmacokinetics (ADME)

Half-life

Not formally established; LL-37 is susceptible to rapid proteolytic degradation in serum and tissue fluids; analog studies suggest an effective in vivo half-life likely on the order of minutes to low tens of minutes under systemic exposure conditions

Clearance

Primarily protease-mediated (serine proteases, matrix metalloproteinases); renal/hepatic clearance not formally characterized for the native peptide

PK–PD note: Systemic pharmacokinetic data for exogenously administered native LL-37 in humans are essentially absent from the peer-reviewed literature. A preclinical pharmacokinetic study of an SE-33 analogue del…

Reading the evidence

• Evidence quality and gaps vary by application — see the cited grades above.
• Indexed-article counts span all evidence tiers, not only completed human trials.
• No first-party human-dosing, efficacy, or benefit claims are made here.

Key reviews & evidence-gap sources

• Yang B et al. Significance of LL-37 on Immunomodulation and Disease Outcome. Biomed Res Int. 2020. — Narrative review; immunomodulation dual role (pro- and anti-inflammatory), cancer.
• Little peptide, big effects: the role of LL-37 in inflammation and autoimmune disease. 2014. — Narrative review of LL-37/mCRAMP in autoimmune/inflammatory pathways.
• LL-37: Cathelicidin-related antimicrobial peptide with pleiotropic activity. 2016. — Narrative review mapping molecular pathways to diseases.
• Antimicrobial Peptides of the Cathelicidin Family: Focus on LL-37 and Its Modifications. Int J Mol Sci. 2025. — Recent narrative review of LL-37 analogs and therapeutic limitations.

5 registered trials — 1 currently recruiting.

—
NCT07280754
Evaluation of 25(OH)D3 and LL-37 Levels in Periimplant Sulcus Fluid

NOT_YET_RECRUITING

—
NCT06219330
Cathelicidin LL-37 Relation to Potentially Malignant Lesions

COMPLETED

—
NCT05054361
Crosstalk Between Mucosal-Associated Invariant T (MAIT) Cells and the Gut Microbiota and Mucosa in the Development of Type 1 Diabetes in Children

RECRUITING

Phase 2
NCT04098562
Efficacy of LL-37 Cream on Bacteria Colonization, Inflammation Response and Healing Rate of Diabetic Foot Ulcers

UNKNOWN

—
NCT04861493
Cathelicidin LL-37 Levels in the GCF and the Saliva of Smokers and Non-smokers With Stage III,IV Periodontitis

COMPLETED

Summary (literature)

In vitro data indicate that LL-37 is cytotoxic to multiple human cell types at concentrations of approximately 1–10 µM, causing membrane disruption, LDH release, and reduced cell viability; hemolytic activity and toxicity to leukocytes have also been reported at micromolar concen…

WADA status

Not specifically listed by name on the WADA 2026 Prohibited List. LL-37 is an endogenous host-defense peptide and does not fall within the explicit S2 category …

Dominant research route: Topical

Topical application to skin/wound surfaces; cited human randomized placebo-controlled trial in hard-to-heal venous leg ulcers (Grönberg et al., 2014) and ex-vivo wound-infection models using LL-37-loaded cubosome carriers

Bioavailability: Local topical delivery to epithelial/wound surfaces; proteolytic degradation in solution is a documented limitation, and carrier formulations (e.g., cubosomes) have been shown to protect LL-37 from enzymatic attack in ex-vivo studies

Most-studied route in humans; the Grönberg 2014 trial is referenced as a randomized, placebo-controlled clinical trial of topical LL-37 for venous leg ulcers. No systemic PK characterized in these studies.

Intranasal instillation in C57BL/6 mice: (1) topical/intranasal LL-37 challenge inducing olfactory epithelium inflammation (Alt et al., 2015); (2) intranasal immunization with MERS-CoV S-RBD-LL-37 fusion as vaccine adjuvant in mice and hDPP4-transgenic mice (Kim et al., 2022)

Bioavailability: Intranasal delivery exploited for mucosal immune induction; fluorescently conjugated LL-37 showed global sinonasal epithelial binding and tissue distribution within 0.5-24 h in mouse mucosa

Studied as a mucosal vaccine adjuvant and as an inflammatory challenge agent in mouse sinonasal models; no human intranasal PK data identified.

No dedicated oral delivery study identified; oral bioavailability of peptide drugs discussed generally as limited by digestive proteolysis and poor intestinal mucosal penetration

Bioavailability: Low oral bioavailability expected for peptide drugs due to degradation by digestive proteolytic enzymes and poor ability to penetrate intestinal mucosa; LL-37 specifically noted to be rapidly degraded by host proteases and serum-binding factors, reducing in-vivo bioavailability

Oral route not established as a studied delivery route for LL-37; stability concern is proteolytic susceptibility rather than characterized oral absorption.

Animal & human figures are kept visibly separate so studied animal doses are never misread as human guidance.

Sorted A–Z by vendor — never by price

Weekly median $/mg from the live vendor crawl.

Researched storefront prices, bucketed

p25 $13.50 · median $14.00 · p75 $17.20 · 7 researched vendors

Legit, COA-backed band: $10.00–$19.00/mg.

Value rule: don't just buy the cheapest — a price under $3/mg is a red flag. Pair price with COA and independent-test grade.

Estimated cost of research (10 mg)

Vial (best researched price)

$106

Bacteriostatic water (generic estimate)

$6

Syringes / supplies (generic estimate)

$12

What each test proves — general guidance, plus this compound's researched purity data

Purity on the current market (researched)

Single published third-party HPLC report for an LL-37 5 mg vial (batch 12-24-0105A, tested Jan 15, 2025) reported 99.645% purity; no aggregate purity range across multiple LL-37 batches/labs was available from retrieved sources.

Independent labs cited for this compound

No FDA recall, seizure, or criminal enforcement action naming LL-37 (Cathelicidin LL-37) specifically was found in FDA warning-letter, recall, or import-alert records retrieved. Related peptide-vendor warning letters (e.g., Gram Peptides, MARCS-CMS 721806, March 31, 2026) cite unapproved-new-drug violations for other peptides but do not name LL-37.

Buyer red-flag checklist

• LL-37 (Cathelicidin LL-37) was placed on FDA's Category 2 'significant safety concerns' bulks list in September 2023, effectively barring compounding under 503A.
• Even after the April 2026 removal from Category 2, LL-37 was NOT moved to Category 1 ('may compound') and remains outside FDA's interim enforcement discretion; HHS indicated LL-37 likely to remain restricted.
• No FDA-approved new drug application exists for LL-37; gray-market vendors market it 'for research use only' while labeling implies human use, mirroring patterns cited in FDA peptide warning letters.
• A published third-party lab report documented an underfilled LL-37 vial (4.23 mg actual vs 5 mg label), illustrating label-claim discrepancies in the unregulated research-peptide market.
• No compound-specific FDA import alert, recall, or criminal seizure naming LL-37 was found; absence of enforcement does not constitute approval.
• Nonclinical research findings cited by FDA/HHS suggest LL-37 could negatively impact male fertility, contributing to its Category 2 safety designation.

GMP vs research-grade: the chemistry (SPPS + HPLC + MS) is identical — the difference is the quality system.

Underdosing / mislabeling: One published third-party lab report (Verified Peptides, batch 12-24-0105A, Jan 15, 2025) measured 4.23 mg actual content versus a 5 mg label claim (~84.6% of label) for an LL-37 vial, indicating underfill/underdosing in that single sample; no independent aggregate prevalence figure (Janoshik/MZ Biolabs/Finnrick) for LL-37 was available from retrieved sources, so prevalence is not estimated.

• An RUO label is not an import exemption — CBP judges actual intended use.
• Lyophilized powder is ambient-stable in transit; temperature control needed for > 7-day transit.
• US-warehouse vendors dodge import scrutiny — they cost more but ship more reliably.

Every item dated & sourced

Not specifically named on the WADA Prohibited List; however, WADA Section S0 prohibits pharmacological substances with no current approval for human therapeutic use, which may encompass LL-37. Verification against the current official list required.

No granted patents identified in current seed. Composition-of-matter coverage is limited given the peptide's synthetic origin.

• IACUC / IRB research context
• RUO buyer responsibilities & documentation
• Veterinary / alternative-use where lawful
• Jurisdiction-aware "who may lawfully obtain"

What people discuss

Reported concerns — discussion, not established effects

Reading caveats

• Self-experimentation without baseline immune markers or controls
• Causation attributed to LL-37 despite confounders (seasonal variation, vitamin D, diet)
• Dosing protocols diverge sharply from published research parameters
• Vendor-affiliated aggregator content present (realpeptides.co)
• Animal brain-injection data extrapolated to systemic human use

Manually researched from reddit, youtube— theme weights are research estimates, not live counts; aggregated & de-identified. No individual posts, quotes, or usernames are ever shown.

Relative research / market volume — populated once the activity stream is wired

Inline tooltips for lyophilized, RUO, EU/mg, SPPS, 503A and more.

Toggle plain-language ↔ scientific in the header.

• How to read a COA
• Free base vs acetate
• Understanding evidence grades

Human cathelicidin antimicrobial peptide derived from hCAP18; disrupts bacterial membranes and modulates innate immune signaling in research models. Approximately 2,484 articles are indexed (literature last scanned 2026-05-29). US regulatory status: Removed from FDA Category 2; awaiting PCAC review; not approved for compounding. Research use only.

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