ll-37 peptide FAQ

LL-37 isn’t scheduled for FDA review until February 2027, so for now, its availability is strictly limited. It can be found in certain wellness clinics and medical spas around the country. One online purveyor that carries it in pharmaceutical grade is Bridgeside Telehealth. We’ve yet to come across another telehealth provider that has it. To get an LL-37 prescription in 2026, you must qualify for an exemption from the Federal Food, Drug, and Cosmetic Act, the set of laws that governs accessibility to restricted peptides. An exemption requires that the requested drug be “compounded for an identified individual patient based on the receipt of a valid prescription order or a notation, approved by the prescribing practitioner, on the prescription order that a compounded product is necessary for the identified patient.” 18 In lay terms, that means a licensed clinician must consider the drug to be medically necessary for the patient, with the caveat that no other, more widely available treatment would be suitable. Future availability hinges on the outcome of the FDA’s review in 2027. If the Administration determines that LL-37 should be moved from Category 2 into Category 1, prospective patients will need only a standard prescription, as they would with mainstream peptides such as semaglutide. Again, we’ll be following developments closely and will update this guide as new information comes to light.

The most likely candidates for LL-37 are people recovering from invasive surgery — around 0.5–3.0% of all surgical patients, by one estimate. 15 Within that cohort are subsets that are at higher risk of infection, and therefore have a greater need for LL-37, than others. For example: 16 The elderly The immunocompromised Current smokers People with diabetes, overweight, or obesity People whose surgeries lasted longer than 2 hours Cancer is another factor that increases one’s risk of developing a postoperative infection, but it also appears to be a contraindication for LL-37 owing to its pro-tumorigenic action. So anyone with a personal or family history of cancer probably would be excluded as a candidate. The same might be said about people with chronic inflammatory health conditions. Even though LL-37 plays a regulatory role in the body’s inflammatory response, it may also exacerbate inflammatory disorders (e.g., psoriasis). 17

Given LL-37’s current restricted status and attendant rarity on the prescription market, we can’t rightly delineate a standard treatment protocol for it. But based on the existing research, we can deduce at least a few aspects of the LL-37 use experience.

LL-37 belongs to a family of antimicrobial peptides called cathelicidins — hence its full and proper name, cathelicidin LL-37 . Cathelicidins occur naturally in animal organisms, as innate components of the immune system. Around 30 cathelicidins have been identified in mammalian species, of which LL-37 is the only one that has yet been found in humans. 1 The “37” part of its name refers to the total number of amino acids in its sequence, and “LL” indicates the first two (leucine). In the human body, cathelicidin LL-37 has both a direct and an indirect antimicrobial function. In the presence of bacteria, viruses, fungi, or parasites, it can bind to and destroy the invading pathogen. Elsewise, it modulates the inflammatory response, directs immune cells to the site of infection, and differentiates T cells into different immune cell types, helping to give the body a better fighting chance against whatever’s ailing it. 2

With regard to safety, LL-37 has a few issues. As of 2026, LL-37 remains on the Category 2 list of bulk drug substances, a roster of substances that the United States Food & Drug Administration (FDA) has identified as posing significant safety risks . The FDA has presented a fourfold reasoning for LL-37’s placement in this category: 11 Immunogenicity: By some routes of administration, LL-37 may trigger an immune response in which the body regards it as a harmful substance, possibly owing to “complexities with regard to peptide-related impurities and API characterization.” Called immunogenicity , this immune response is similar to an allergic reaction and can be similarly life-threatening. “Detrimental effects on male reproduction”: Nonclinical studies suggest that LL-37 is capable of spermicidal activity. These studies have examined the peptide’s effects on both animal and human sperm. 12 Tumorigenesis: According to some research studies, LL-37 may spur tumor growth in the ovaries, lungs, breasts, prostate, pancreas, and skin. 13 Lack of safety studies: Per the FDA, there isn’t enough “safety-related information regarding cathelicidin LL-37 to know whether the drug would cause harm when administered to humans.” Recall, though, that a 2014 randomized, placebo-controlled trial reported “no safety concerns regarding local or systemic adverse events.” Though that would seem to contradict the FDA’s official statements about LL-37, it’s still just one study. As LL-37 will soon come under FDA review for potential recategorization, we may see an increase in human research on the peptide, revealing whether it’s safer or more dangerous than the existing literature suggests. We’ll be following such developments and updating this guide accordingly.

Over the past two decades, Innerbody Research has helped tens of millions of readers make more informed decisions about staying healthy and living healthier lifestyles. At this writing, we’ve cumulatively spent over 1,000 hours researching therapeutic peptides. Not just the mainstream weight-loss ones, either, but also the obscure and the experimental, like LL-37. Each piece we’ve written is built upon the available scientific literature on the subject. When possible, we’ve also incorporated the ground-view perspectives of doctors and patients — people who know intimately how peptides work and whom they might best serve. Additionally, like all health-related content on this website, this guide was thoroughly vetted by one or more members of our Medical Review Board for accuracy and will continue to be monitored for updates by our editorial team.

Refrigerate it immediately and use it only if the exposure was less than 12 hours. But expect 15–25% potency loss. LL-37 oxidises rapidly at methionine residues above 15°C, and the degradation is irreversible once it occurs. If the peptide was out for more than 24 hours, discard it. Visual clarity means nothing. Oxidised methionine sulfoxide looks identical to intact methionine but has lost the hydrophobic character required for membrane insertion. Running a pilot assay with a known positive control is the only way to confirm retained activity.

Use a validated cold chain shipping container with gel packs pre-frozen to −20°C, and include a temperature datalogger to verify the peptide never exceeded 8°C during transit. Lyophilised peptide tolerates brief temperature fluctuations better than reconstituted solution, but any excursion above 25°C for more than 6 hours begins irreversible degradation even in powder form. For reconstituted peptide, ship on dry ice (−78°C) in insulated Styrofoam. Gel packs alone will not maintain 2–8°C for more than 18–24 hours depending on ambient temperature.

Aliquot the remaining solution into single-use volumes and freeze at −80°C immediately. This arrests further degradation and extends usable lifespan by 3–6 months. Each aliquot should be thawed only once; repeated freeze-thaw cycles cause ice crystal formation that physically disrupts the peptide structure. Label each aliquot with the reconstitution date and freeze date. For critical experiments, run a fresh standard curve using a newly reconstituted reference vial to confirm your frozen aliquots retained expected activity.

No. Mouse models should use mouse CRAMP peptide, not human LL-37, unless the research question specifically examines human peptide pharmacokinetics in a murine system. Mouse and human cathelicidins have different receptor binding profiles, tissue distribution, and proteolytic stability. Human LL-37 injected into mice will produce some antimicrobial effects via direct membrane disruption, but immunomodulatory signaling through FPR2 and EGFR will not replicate human responses because murine receptor orthologs have lower binding affinity for the human peptide sequence. If your experimental goal is to model human LL-37 immune function, use human cell assays or humanized mouse models. Wild-type mouse studies require mouse CRAMP for physiological relevance.

Yes. Purity directly affects reproducibility and dose-response accuracy in immune signaling studies. A 95% pure LL-37 preparation contains up to 5% truncated peptides, deletion sequences, or synthesis byproducts that may have different antimicrobial potency or receptor binding affinity. For antimicrobial killing assays where high micromolar doses are used, 95% purity may be acceptable. For receptor signaling studies at nanomolar concentrations (FPR2 calcium flux assays, chemotaxis), impurities at 5% can introduce confounding ligands that skew dose-response curves. Research-grade LL-37 should meet ≥98% purity by HPLC for publication-quality data. This is the standard Real Peptides guarantees, with every batch tested for sequence fidelity and deletion variant contamination before release.

Choose one format and apply it uniformly throughout your submission. Regulatory agencies like the FDA do not require a specific hyphenation standard for peptide names. They require consistency within a single filing. If your initial investigational new drug (IND) application referred to the compound as LL37, continue using LL37 in all subsequent amendments, annual reports, and correspondence. If you accidentally switch between LL37 and LL-37 mid-document, include a clarifying note in the submission cover letter stating both names refer to the same 37-amino-acid cathelicidin peptide and provide the full amino acid sequence to eliminate ambiguity. Consistency matters more than which specific format you choose.

Use human LL-37 unless the protocol explicitly requires the hCAP-18 precursor or a non-human ortholog like mouse CRAMP. The vast majority of published cathelicidin research used the active LL-37 fragment because the precursor has negligible bioactivity in vitro. If replicating a published study, check the methods section for peptide supplier and catalog number. If the original study used a 4–5 kDa peptide, it was LL-37; if 18 kDa, it was hCAP-18. When in doubt, LL-37 is the correct choice for antimicrobial assays, immune cell migration studies, and receptor binding experiments.

Proceed with the 'LL-37' product if the Certificate of Analysis confirms the full 37-residue sequence and ≥95% purity. The protocol author used 'peptide' as a molecular class descriptor, not a distinct chemical variant. Cross-reference the paper's methods section for CAS number (should be 154947-66-7) or molecular weight (4493 Da) to confirm alignment. If the supplier cannot provide sequence verification or the mass spectrum shows a different molecular weight, contact the protocol's corresponding author to clarify whether they used authentic LL-37 or a modified analog. Substituting unverified peptides into established protocols invalidates comparative data and wastes research resources.

Request Certificates of Analysis for both catalogue entries and compare the amino acid sequence, molecular weight, and purity data. If the sequence is identical (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES), you're being offered the same molecule under duplicate SKUs. Select based on price per milligram and endotoxin specification, not the name. If the sequences differ or one listing lacks mass spectrometry verification, the lower-priced option is likely a truncated analog or unverified synthesis product that won't reproduce published LL-37 data. Authentic LL-37 costs $180–$320 per milligram at research-grade purity; significant price deviations below $150/mg suggest quality compromise or nomenclature misrepresentation.

Check the experimental conditions and peptide purity, not the name. Apparent conflicts between LL37 and LL-37 studies almost always trace to differences in assay methodology, cell line selection, peptide concentration ranges, or post-synthesis modifications rather than the nomenclature itself. For example, some early LL-37 studies used crude synthetic peptides with 70–85% purity, while modern LL37 studies use HPLC-purified material at >98% purity. The impurity profile affects bioactivity far more than the hyphen. If you encounter conflicting MIC values or receptor-binding affinities between studies, compare the actual experimental protocols and peptide characterization data rather than assuming the name difference indicates a distinct molecule.

Contact your supplier to confirm the exact peptide sequence and species origin. If the supplier documentation lists 'human cathelicidin, active fragment, 37 amino acids,' it is LL-37. If documentation does not specify 'active fragment' or lists molecular weight as 18 kDa, you may have received the inactive hCAP-18 precursor, which will not produce antimicrobial or immunomodulatory effects in standard assays. Request a certificate of analysis showing mass spectrometry confirmation of the 37-amino-acid sequence and N-terminal leucine-leucine residues. This is the definitive verification that cathelicidin same as LL-37 applies to your order.

Order the LL37. They are the same peptide. Verify the amino acid sequence on the supplier's certificate of analysis matches the 37-residue cathelicidin fragment (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES). If the sequence, molecular weight (4493.3 Da), and purity specifications match your protocol requirements, the hyphen difference is irrelevant. Reputable peptide manufacturers synthesize to sequence, not to name formatting, so the biological activity will be identical. We've seen researchers delay studies by weeks trying to source "LL-37" specifically when their institution already had LL37 in inventory. The procurement confusion serves no scientific purpose.

Check salt concentration first. Physiological NaCl levels (150 mM) reduce LL-37 antimicrobial activity by 40–70% compared to low-salt assay buffers used in many published MIC determinations. If your assay medium contains ≥100 mM NaCl and you're comparing results to a paper that used 10 mM phosphate buffer, the potency difference reflects assay conditions, not peptide quality. Second, verify storage time post-reconstitution. LL-37 oxidizes at methionine-4 within 72 hours at 4°C, progressively losing activity. If you reconstituted more than 4 days prior to the assay, prepare a fresh aliquot from lyophilized stock. Third, confirm your supplier provided mass spectrometry data. Peptides sold without MS verification may be LL-23 (23-residue truncation) or other cathelicidin fragments with 60–80% lower potency that elute at similar HPLC retention times.