Read This First
This page is not built on clinical evidence. It is built on the regulatory record and on what is known about the peptide's chemistry and biology. What LL-37 does, and the two wound trials that tested it, are covered on the library entry; this page is about what is in a vial labelled LL-37 and why this particular molecule is a poor candidate for injecting on trust.
LL-37 is a 37-residue, strongly cationic, membrane-active peptide that the body makes and controls tightly, that is cytotoxic to human cells at higher concentrations, and that has never been given systemically to a person in any study.1 The FDA's compounding entry for it names male reproductive harm and tumour promotion from nonclinical work.2 Those are the facts a sourcing page for this compound has to start from.
Legal Status
Where Does LL-37 Stand?
Approved nowhere. No marketing authorisation, no monograph, and not a component of any approved drug. The one drug programme, Promore Pharma's topical ropocamptide for venous leg ulcers, stopped after a negative Phase 2b in 2021.3
In the United States, cathelicidin LL-37 was placed in Category 2 of the FDA's interim compounding policy in September 2023 and is now listed among substances nominated but withdrawn, with the original text unchanged.2 It was not among the seven peptides the Pharmacy Compounding Advisory Committee considered in July 2026, so no vote concerns it.4 No pharmacy in the United States has a lawful basis on which to compound it.
What Does the FDA Say About It?
The entry, in full: compounded drugs containing cathelicidin LL-37 "may pose risk for immunogenicity for certain routes of administration and may have complexities with regard to peptide-related impurities and API characterization. FDA lacks sufficient safety-related information regarding cathelicidin LL-37 to know whether the drug would cause harm when administered to humans. Nonclinical research findings suggest detrimental effects on male reproduction and that this drug can be protumorigenic in some tissues."2
Most entries on that list say the agency lacks information. This one also says what the information it has points to.
Product Identity
What Makes This Peptide Hard to Make and Verify?
Length and charge. Thirty-seven residues means 36 coupling steps, each an opportunity for a deletion sequence of nearly identical mass and behaviour. Six lysines and five arginines make the peptide highly cationic, which is how it binds bacterial membranes and also why it aggregates readily, sticks to surfaces, and is prone to forming oligomers in solution.1 The FDA's phrase for the consequence is "complexities with regard to peptide-related impurities and API characterization."2
Aggregation is not an abstract quality point here. Aggregated peptide is the classic immunogen, and LL-37 is a molecule the immune system already recognises: it is a T-cell autoantigen in psoriasis.5 Injecting aggregated LL-37 under the skin is, mechanistically, an attempt to raise an immune response to a self-protein.
The Concentration Problem
LL-37 kills bacteria by disrupting membranes, and at higher concentrations it does the same to human cells. That therapeutic window is narrow enough that in the first-in-human wound trial the highest topical concentration, 3.2 mg/mL, performed no better than placebo while the two lower ones helped, which the authors attributed at least partly to cytotoxicity.6 A gray-market vial has a concentration on its label and no study to say whether that concentration, at an injection site, is in the window or above it.
Purity Testing Versus Identity Testing
| Test | Question it answers | Question it cannot answer |
|---|---|---|
| HPLC purity | What proportion of the sample is one main peak | Whether that peak is full-length LL-37 or a co-eluting deletion sequence; whether it is aggregated |
| Mass spectrometry identity | Whether the mass matches, about 4,493 daltons | How much of the sample it represents; whether methionine has oxidised, which adds 16 daltons and reduces activity |
| Endotoxin assay | Whether bacterial cell-wall fragments are present | Identity; and LL-37 binds endotoxin, which can interfere with the assay itself |
| Aggregate analysis | Whether the peptide has oligomerised | Almost never offered; for this peptide it is the question that matters most |
Certificates of Analysis
What a Certificate Is
A laboratory report on one batch. Read it for the laboratory's independence from the seller, the lot number and whether it matches the vial, the date, and which tests were actually run rather than mentioned. For LL-37, note whether the endotoxin method accounts for the peptide's own endotoxin-binding, and whether anything at all is said about aggregation.
What It Cannot Establish
That the vial in hand came from the batch tested. Its value rests on a chain of custody the buyer cannot inspect. A certificate is a PDF, and nothing about the format prevents reuse or fabrication; the FDA has documented fabricated labels on gray-market peptide products.7
"Research Use Only"
Does the Label Change Anything?
No. It is a liability position adopted by the seller, not a regulatory category. The FDA has held in warning letters that the disclaimer does not survive product copy establishing human use.8 LL-37 is, unusually, a genuine research reagent with a large legitimate market in laboratories. That is exactly why the label is credible on a supplier's website and not on a page describing "immune support" with a weekly injection schedule.
The Route Problem
Why Does It Matter That the Trials Were Topical?
Because every human study of LL-37 put it on a wound or into a tumour, where it acts locally and is cleared locally.69 Subcutaneous injection for systemic effect is a different exposure, and for this molecule the difference is not only quantitative. The body keeps LL-37 compartmentalised: stored as an inactive precursor, released and cleaved where it is needed, and degraded quickly. Systemic LL-37 is what happens in disease, not health; elevated circulating levels are a feature of sepsis and of several inflammatory conditions.1 A weekly injection is an attempt to produce that state on purpose.
Storage and Handling
What Is Known
No manufacturer-validated storage specification exists for any product a consumer can buy. Research suppliers ship LL-37 lyophilised and recommend frozen storage of the powder and of aliquoted solutions, avoiding repeated freeze-thaw, because the peptide aggregates and adsorbs to plastic in solution. A cationic peptide of this length in a multi-dose vial at refrigerator temperature for weeks is being kept under conditions no supplier recommends.
Multi-Dose Vials
The FDA's guidance for compounded injectables is to discard a multi-dose vial within 28 days of first use regardless of what remains, and to use a new sterile needle and syringe for every dose.7 LL-37 is an antimicrobial, which some sellers cite as a reason the rule matters less. It is also cytotoxic and self-aggregating, which is a reason it matters more.
Signs to Stop Rather Than Proceed
A solution that is cloudy or develops particles, which in a cationic peptide of this length is aggregation, and aggregated LL-37 is an immunogen
Injection-site pain, redness or tissue damage beyond the ordinary, given the peptide's cytotoxicity at higher concentrations
Any new or worsening psoriasis, rosacea or other inflammatory skin condition, given LL-37's role in both510
A certificate with a single purity figure and no aggregation or endotoxin data
Use by anyone with a personal or family history of the cancers in which LL-37 is tumour-promoting: ovarian, lung, breast, prostate, pancreatic, skin, melanoma11
Community Language
LL-37, cathelicidin, hCAP18
The peptide, the family it belongs to, and the precursor protein it is cleaved from. The vial contains the first; the body makes the third.
Ropocamptide
Promore Pharma's name for its topical LL-37 drug candidate. Not for sale; its programme stopped in 2021.
Antimicrobial peptide, AMP
The class. Membrane-active by design, which is why the therapeutic window is narrow.
Biofilm buster
Marketing language for LL-37's in vitro activity against bacterial biofilms. No human study has tested it for that purpose by any route.
Category 2
The FDA's interim classification for nominated compounding substances that may present significant safety risks. LL-37's entry is one of the few that names specific harms.2
Certificate of analysis
A laboratory report on one batch. It describes the batch tested, not necessarily the vial received, and for this peptide almost never the property that matters.
Related ONPEPS Coverage
LL-37 library entry: the immunology, the two wound trials and the cancer question
Compounded, gray market and counterfeit semaglutide: what the regulators have documented
Sources
Vandamme D, Landuyt B, Luyten W, Schoofs L. A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cell Immunol. 2012;280(1):22-35. Paywalled. pubmed.ncbi.nlm.nih.gov/23246832
US Food and Drug Administration. Category 2 of the Bulk Substances Nominated Under Sections 503A or 503B of the Federal Food, Drug, and Cosmetic Act. Entry for cathelicidin LL-37. Content current as of 22 April 2026. fda.gov
Mahlapuu M, Sidorowicz A, Mikosinski J, Krzyżanowski M, Orleanski J, Twardowska-Saucha K, et al. Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial. Wound Repair Regen. 2021;29(6):938-950. Open access. pubmed.ncbi.nlm.nih.gov/34687253
US Food and Drug Administration. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. Docket FDA-2025-N-6895. fda.gov
Lande R, Botti E, Jandus C, Dojcinovic D, Fanelli G, Conrad C, et al. The antimicrobial peptide LL37 is a T-cell autoantigen in psoriasis. Nat Commun. 2014;5:5621. Open access. pubmed.ncbi.nlm.nih.gov/25470744
Grönberg A, Mahlapuu M, Ståhle M, Whately-Smith C, Rollman O. Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial. Wound Repair Regen. 2014;22(5):613-621. Paywalled. pubmed.ncbi.nlm.nih.gov/25041740
US Food and Drug Administration. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. Drug Alerts and Statements. Cited for the agency's general guidance on multi-dose vials and fabricated labels. fda.gov
US Food and Drug Administration. Warning Letter: Gram Peptides. MARCS-CMS 721806, 31 March 2026. fda.gov
ClinicalTrials.gov. NCT02225366. Intratumoral Injections of LL37 for Melanoma. Sponsor M.D. Anderson Cancer Center. Phase 1/2, 4 participants, completed. Record retrieved 16 September 2026. clinicaltrials.gov/study/NCT02225366
Yamasaki K, Di Nardo A, Bardan A, Murakami M, Ohtake T, Coda A, et al. Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea. Nat Med. 2007;13(8):975-980. Open access. pubmed.ncbi.nlm.nih.gov/17676051
Chen X, Zou X, Qi G, Tang Y, Guo Y, Si J, et al. Roles and mechanisms of human cathelicidin LL-37 in cancer. Cell Physiol Biochem. 2018;47(3):1060-1073. Open access. pubmed.ncbi.nlm.nih.gov/29843147
Not Medical Advice
LL-37 holds no marketing authorisation for human use in any jurisdiction and has never been given systemically to a person in a study. If you are already using a product obtained outside a pharmacy, the route back to oversight is a clinician who knows what you have taken.
Regulatory sources verified 16 September 2026. The compounding record changes frequently. Re-verify before relying on any statement here.