--- title: "LL-37 Peptide: Benefits, Dosage, Side Effects & Uses" description: "LL-37 is the only human cathelicidin, a defense peptide switched on by vitamin D. How it works, what the wound trials show, side effects and cancer questions." canonical: "https://www.vitalsvault.com/peptides/ll-37" last-updated: 2026-08-22 --- # LL-37 Peptide: Benefits, Dosage, Side Effects & Uses > LL-37 is the only human cathelicidin, a defense peptide switched on by vitamin D. How it works, what the wound trials show, side effects and cancer questions. ![A Peruvian-Japanese woman, 36, sleek black bob, round cheeks, stands under a clear umbrella on a quiet residential side street of brownstones and…](https://www.vitalsvault.com/_next/image?url=%2Fpublic-v3%2Fshoot%2Fpeptides%2Fpep-ll37.webp&w=3840&q=75&dpl=shadow-production-f0162cb4d465-40992538108-1) Peptide Guide · Immune health # LL-37 Human cathelicidin antimicrobial peptide (hCAP18 fragment) LL-37 is one of your body’s own antibiotics, and vitamin D helps set how much you make. Too little leaves a gap in defense, and too much is linked to psoriasis and rosacea. [Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist)[Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) Free to join · One email when peptide care opens · Most lab results in 3–5 business days Studied forWound healing, antimicrobial defense and skin inflammation EvidenceEarly human data Taken asAs prescribed by a clinician Studied forWound healing, antimicrobial defense and skin inflammation EvidenceEarly human data Taken asAs prescribed by a clinician ## LL-37, in short LL-37 is a 37-amino-acid peptide and the only cathelicidin humans make. Skin and white blood cells release it to kill microbes and to signal immune cells, and vitamin D helps switch on its gene. It is studied for chronic wounds, infection and skin inflammation. Human evidence comes mostly from small topical trials in chronic wounds, with mixed results. Medically reviewed by [Robert Lufkin, MD (opens in a new tab)](https://www.robertlufkinmd.com/) Chief Medical Officer, Vitals Vault · Updated October 29, 2026 · 17 sources ## At a glance Early human data TypeAntimicrobial peptide, 37 amino acids[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998) Made bySkin cells and white blood cells, cut from a larger protein called hCAP18[7](https://www.vitalsvault.com/peptides/ll-37#source-piktel-2016)[13](https://www.vitalsvault.com/peptides/ll-37#source-dombrowski-2012) Switched on byVitamin D, through the vitamin D receptor[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005) Studied forChronic wounds, antimicrobial defense, skin inflammation[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[6](https://www.vitalsvault.com/peptides/ll-37#source-fabisiak-2016) Best human dataTopical trials in venous leg ulcers[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) FDA statusNot approved. Its compounding nomination was withdrawn from FDA’s category 2 list; FDA still lists safety risks[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks) ## Before you consider LL-37 - Safety Topical LL-37 was well tolerated in leg ulcer trials. That does not cover injections, and FDA says it lacks safety information on LL-37.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks) [Side effects and safety](https://www.vitalsvault.com/peptides/ll-37#safety) - Legal status Not FDA approved. It is not among the six peptides covered by FDA’s October 2026 policy, and FDA’s page lists immunogenicity and safety concerns.[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks)[17](https://www.vitalsvault.com/peptides/ll-37#source-ncpa) [FDA status](https://www.vitalsvault.com/peptides/ll-37#fda-status) - How it’s taken In trials, LL-37 was applied to leg ulcers as a gel under a clinical protocol. The trials did not test injection.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks) [Forms and dosage](https://www.vitalsvault.com/peptides/ll-37#how-taken) ## How does LL-37 work? LL-37 is both a germ killer and a messenger. What it does depends on how much is present and where. - ### Damages germs It folds into a shape that goes with its ability to kill both major groups of bacteria.[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998) - ### Directs immune cells It attracts and activates immune cells and shapes inflammation, so it has effects in the airway, gut and skin.[6](https://www.vitalsvault.com/peptides/ll-37#source-fabisiak-2016) - ### Linked to vitamin D Active vitamin D strongly turns up the gene that makes LL-37 in immune cells. This link is specific to primates.[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005) ## LL-37 benefits: what it is studied for Human data are limited to a few wound trials. Everything else is laboratory or review-level. 1. Human study01 ### Chronic venous leg ulcers In a first-in-human trial of 34 people, the lowest strength of topical LL-37 raised the healing rate about six-fold over placebo. The highest strength showed no detectable advantage.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014) 2. Human study02 ### Larger ulcers A phase 2b trial of 148 people found no significant gain overall. A post hoc look found benefit in ulcers of at least 10 cm2, and the authors called for a new trial.[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) 3. Lab study03 ### Antimicrobial defense In cell culture, LL-37 cut the growth of tuberculosis bacteria by about three-quarters, and vitamin D raised its gene in immune cells. This is laboratory work.[4](https://www.vitalsvault.com/peptides/ll-37#source-martineau-2007)[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005) ## What the research shows Early human data 1. 1 · Cells in a lab Studied Kills both major groups of bacteria in the lab, and cut tuberculosis bacteria growth in cell culture by about three-quarters.[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998)[4](https://www.vitalsvault.com/peptides/ll-37#source-martineau-2007) Shows a mechanism 2. 2 · AnimalsNot cited This guide cites no findings at this level. Shows an effect in a body 3. 3 · People Studied Topical LL-37 raised leg ulcer healing in a 34-person trial, but a 148-person trial found no overall benefit.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) Shows it works in people The wound trials are the main human evidence. The first trial found a significant benefit at the lowest strength, and the larger phase 2b trial did not reach significance overall. A 2023 trial of an LL-37 cream in diabetic foot ulcers reported faster healing. The signal in larger ulcers came from a post hoc analysis, which is a hypothesis and not a result. These trials tested topical LL-37 on wounds, not the injections sold online.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[10](https://www.vitalsvault.com/peptides/ll-37#source-miranda-2023)[7](https://www.vitalsvault.com/peptides/ll-37#source-piktel-2016) The cancer picture is mixed. A review of experimental studies found LL-37 overexpression promoted ovarian, lung and breast cancer and suppressed tumor growth in colon and gastric cancer models, findings that do not show what giving LL-37 does in people. FDA’s page separately notes possible tumor promotion in some tissues.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[10](https://www.vitalsvault.com/peptides/ll-37#source-miranda-2023)[7](https://www.vitalsvault.com/peptides/ll-37#source-piktel-2016) The full guide to LL-37 9 min read · Medically reviewed by Robert Lufkin, MD ## Your skin was making antibiotics long before penicillin Every time you cut your finger, your skin starts making an antibiotic. Skin cells release antimicrobial peptides that form a chemical shield on the surface, and in humans one of the most studied is LL-37. The name is simple bookkeeping. It starts with two leucines, written LL, and it is 37 amino acids long. LL-37 is the only cathelicidin humans make. Cells build a larger protein called hCAP18 and cut LL-37 from its tail end when it is needed. Skin cells and white blood cells are major sources, and antimicrobial peptides as a group are concentrated in the mucus layers that line the airway and gut, where microbes first try to settle. It does two jobs at once. It kills bacteria directly, across both major families, Gram-positive and Gram-negative. And it calls in and directs immune cells, shaping inflammation and repair. That double life explains both its promise and its problems. A drug company has developed synthetic LL-37 as a wound gel under the name ropocamptide, and its trials tested that gel on leg ulcers. A separate team tested an LL-37 cream on diabetic foot ulcers. Online, LL-37 is sold for injection and for gut, skin and immune goals, uses the trials did not examine.[13](https://www.vitalsvault.com/peptides/ll-37#source-dombrowski-2012)[7](https://www.vitalsvault.com/peptides/ll-37#source-piktel-2016)[6](https://www.vitalsvault.com/peptides/ll-37#source-fabisiak-2016)[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[10](https://www.vitalsvault.com/peptides/ll-37#source-miranda-2023) ## How LL-37 works: a shape-shifting antibiotic In plain water, LL-37 is floppy, with no fixed shape. Add the salts found in body fluids, such as bicarbonate, and it coils into a helix. In a 1998 study in Stockholm, how helical it became tracked how well it killed bacteria. The same chemistry carries a warning. At higher concentrations, LL-37 was toxic to human cells as well as bacteria, and in fluids that mimic blood plasma it held its active helical shape. In the same experiments, human serum inhibited both its antibacterial and its toxic effects, one lab clue to how the body keeps it in check. Context, in other words, decides what LL-37 does. Its second role is as a messenger. LL-37 attracts immune cells and changes how they behave, which is why it shows up in research on the airway, the gut and the skin. Reviewers describe it as pleiotropic, meaning one molecule with many effects, and they see real potential for drug development. Acid matters too. Below a pH of about 5, LL-37 gradually loses its helix, and at very high acidity it unfolds completely. Where in the body it is released, and in what chemical surroundings, shapes how active it is.[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998)[6](https://www.vitalsvault.com/peptides/ll-37#source-fabisiak-2016) ## LL-37 and vitamin D: a wiring only primates have In 2005, researchers at UCLA and Cedars-Sinai showed that active vitamin D switches on the human cathelicidin gene directly. The vitamin D receptor binds a response element in the gene’s promoter, and the gene switched on in immune cells, skin cells and colon cells. Then they compared genomes. In primates, that vitamin D response element sits inside a short interspersed nuclear element, a stretch of repeated DNA that copied itself around the genome long ago. Mice, rats and dogs lack it, and vitamin D did not switch on the gene in mouse cells. Somewhere in primate evolution, a piece of mobile DNA wired vitamin D to one of our antibiotics. A year later, a study in Science showed the circuit at work. When immune sensors on human macrophages detected tuberculosis bacteria, the cells made more vitamin D receptor and more of the enzyme that activates vitamin D, which drove cathelicidin production and killing of the bacteria inside the cells. In mice, the same job falls mainly to nitric oxide. Blood from African-American donors, who had lower vitamin D, supported cathelicidin production less well. Two practical points follow. Mouse studies cannot model this link. And vitamin D clearly takes part in switching on the gene in human cells. These studies do not show how changing a person’s vitamin D status changes their working LL-37 or their protection from infection.[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005)[3](https://www.vitalsvault.com/peptides/ll-37#source-liu-2006) ## LL-37 and infection: what the lab work shows Tuberculosis is the infection where the vitamin D story is best mapped. In human immune cells infected with mycobacteria, active vitamin D slowed bacterial growth in a dose-dependent way, and it did so without relying on the usual inflammatory signals. It strongly raised the cathelicidin gene. Added directly, LL-37 cut the growth of tuberculosis bacteria in culture by 75.7%. The researchers concluded that vitamin D helps protect against tuberculosis partly through antimicrobial peptides such as this one. These are cell experiments, and they explain a mechanism more than they predict a treatment. The human infection trial cited here used a different product: an oral, engineered bacterium that makes LL-37, which shortened the time to a negative COVID-19 test in a 238-person open-label trial. That says nothing about the purified LL-37 injections sold online, which no study cited here has tested against infection.[4](https://www.vitalsvault.com/peptides/ll-37#source-martineau-2007)[3](https://www.vitalsvault.com/peptides/ll-37#source-liu-2006)[12](https://www.vitalsvault.com/peptides/ll-37#source-zhao-2023) ## LL-37 for chronic wounds: the leg ulcer trials Venous leg ulcers are among the most common chronic wounds, and many do not fully heal with compression bandaging alone. That made them the first target for synthetic LL-37. In a 2014 first-in-human trial, 34 people with hard-to-heal ulcers had a placebo run-in period, then four weeks of LL-37 gel at one of three strengths or placebo. The lowest strength stood out. Its healing rate was about six times placebo’s, a significant difference, and average ulcer area shrank by 68%. The middle strength’s three-fold rise missed significance, though ulcers on it shrank by 50%. The highest strength showed no detectable advantage over placebo. There were no local or systemic safety concerns. The follow-up was larger and more sobering. The phase 2b HEAL LL-37 trial enrolled 148 people, average age 67.6, whose ulcers had lasted a median of 20 months, all on compression therapy. Across the whole group, the trial detected no significant improvement in healing compared with placebo. A post hoc analysis found significant benefit in people with large ulcers, at least 10 cm2, which are known to heal poorly. Several authors worked for the developer, and they called for a new trial powered to test that group. Until then it is a hypothesis.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) ## Why more LL-37 is not better The first wound trial carries a lesson easy to miss. The weakest gel produced the largest effect, the middle strength a smaller one that missed significance, and the strongest no detectable advantage. With LL-37, more did not mean better. The lab work suggests why that might be. At higher concentrations, LL-37 becomes toxic to human cells, not only to bacteria. A molecule that helps at a low level can damage the very tissue it is meant to protect when the dose climbs. This explanation is a hypothesis; the trial did not test why the top strength failed. Skin disease offers the same lesson from the body’s own side. In psoriasis and rosacea, excess or misprocessed cathelicidin is implicated in the inflammation, though in psoriasis it can push some immune pathways up and others down. For anyone tempted by injections, the point is that LL-37 has a working range, and no study cited here has defined that range for injected use in people.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998)[13](https://www.vitalsvault.com/peptides/ll-37#source-dombrowski-2012)[14](https://www.vitalsvault.com/peptides/ll-37#source-coda-2013) ## LL-37 in psoriasis and rosacea Normally, the immune system ignores DNA from your own dying cells. In psoriasis, that tolerance breaks down. A 2007 study in Nature found that LL-37, overproduced in psoriatic skin, binds this self-DNA into dense clumps that plasmacytoid dendritic cells take up and mistake for a viral threat. The cells pour out type I interferons and the inflammation feeds itself. The story then gets more complicated. Vitamin D analogue creams and UVB light therapy calm psoriasis, yet both strongly raise cathelicidin in the skin. And inside skin cells, LL-37 binding to self-DNA can actually quiet a different inflammatory alarm. Researchers describe its role in psoriasis as contrasting, not simply harmful. Rosacea points in one direction. Excess cathelicidin and kallikrein 5, a skin enzyme, have been proposed as drivers of the condition. In a 2013 study, people with rosacea treated with azelaic acid gel had lower cathelicidin and kallikrein 5 gene activity in their skin.[5](https://www.vitalsvault.com/peptides/ll-37#source-lande-2007)[13](https://www.vitalsvault.com/peptides/ll-37#source-dombrowski-2012)[14](https://www.vitalsvault.com/peptides/ll-37#source-coda-2013) Know your baseline before any peptide 120+ lab tests at Quest Diagnostics, every result reviewed by a licensed clinician. Most results in 3–5 business days. A baseline today gives your clinician something to compare against if you start LL-37 later. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans)[Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist) Full refund before your blood draw · No membership ## Does LL-37 promote cancer? It depends on the tissue Chronic infection, inflammation and tissue repair are all linked with tumor growth, and LL-37 is involved in each, so researchers have looked closely at its role in cancer. The answer, from a 2016 review, is that it cuts both ways. In experimental models reviewed in 2016, high levels of LL-37 promoted the development and progression of ovarian, lung and breast cancers. In colon and gastric cancer models, it suppressed tumor growth. None of this shows what giving LL-37 does to cancer risk in a person. The difference seems to come from which receptors each cancer type carries, since LL-37 acts on several of them. FDA’s April 2026 compounding page reached a cautious version of the same conclusion, noting nonclinical evidence that LL-37 can promote tumors in some tissues. For anyone with a personal history of cancer, that is a reason to talk to an oncologist before considering it.[7](https://www.vitalsvault.com/peptides/ll-37#source-piktel-2016)[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks) ## What we know about LL-37 in people Most of what we know about LL-37 in people concerns the version your body makes. Human cells, tissue and blood samples show that vitamin D switches on its gene, that macrophages use it to kill tuberculosis bacteria, and that it is overproduced in psoriasis and rosacea. That is a detailed picture of natural biology. As a medicine, the core record is two trials of a gel on venous leg ulcers, 34 people in the first and 148 in the second. The first found faster healing at the lowest strength, and the second missed its overall goal, leaving a subgroup signal in large ulcers to be tested again. A 2023 Indonesian trial added a cream for mildly infected diabetic foot ulcers and reported faster healing. Outside wounds, the human record is thin and specialized. LL-37 has been injected directly into melanoma skin metastases in an early-phase cancer trial, and one reported patient developed widespread skin lesions that cleared after stopping. An oral engineered bacterium that makes LL-37 was tested in COVID-19. None of that covers the injections sold for gut health, immunity or recovery, whose claims borrow from cell biology and a wound gel.[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005)[3](https://www.vitalsvault.com/peptides/ll-37#source-liu-2006)[5](https://www.vitalsvault.com/peptides/ll-37#source-lande-2007)[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[10](https://www.vitalsvault.com/peptides/ll-37#source-miranda-2023)[11](https://www.vitalsvault.com/peptides/ll-37#source-dolkar-2018)[12](https://www.vitalsvault.com/peptides/ll-37#source-zhao-2023) ## LL-37 side effects and safety As a gel on wounds, LL-37 has a clean record so far. Both leg ulcer trials found it safe and well tolerated, with no local or systemic safety concerns in the first trial. Those results apply to a topical product in a supervised trial. Injected LL-37 is a different matter. FDA’s compounding page lists it among withdrawn category 2 nominations, warns of immunogenicity and impurities, and cites nonclinical findings of harm to male reproduction and possible tumor promotion. Lab studies add that higher concentrations are toxic to human cells, and a case report from a melanoma injection trial described widespread skin lesions that resolved after treatment stopped. People with psoriasis, rosacea or another inflammatory skin or autoimmune condition, anyone with a cancer history, and anyone pregnant, breastfeeding or trying to conceive should treat LL-37 with particular caution and talk to a clinician first.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks)[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998)[5](https://www.vitalsvault.com/peptides/ll-37#source-lande-2007)[11](https://www.vitalsvault.com/peptides/ll-37#source-dolkar-2018) ## Labs that matter for your own LL-37 Vitamin D comes first. The 25-hydroxyvitamin D test measures the main circulating marker of your vitamin D status, the raw material immune cells activate to switch on the cathelicidin gene, and in lab studies blood with low vitamin D supported cathelicidin production poorly. hs-CRP is a nonspecific marker of inflammation, and a white blood cell count gives a basic read on your immune cells. Neither measures LL-37, and the studies here do not call for zinc testing to change it; these are general context a clinician reviews for their own reasons. This is how Vitals Vault approaches immune health. A blood panel comes first, a licensed clinician reviews your results and history, and the simplest, best-supported changes come before anything experimental.[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005)[3](https://www.vitalsvault.com/peptides/ll-37#source-liu-2006) ## Where LL-37 stands in 2026 LL-37 is not an FDA-approved drug. FDA’s April 2026 compounding safety page lists cathelicidin LL-37 among substances previously in category 2 whose nominations were withdrawn, and still describes its possible safety risks. Withdrawal is not approval, and it leaves LL-37 outside the interim policy that applies to category 1. It is not among the six peptides covered by FDA’s October 2026 enforcement discretion, and vials sold online as research use only are not made for people.[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks)[16](https://www.vitalsvault.com/peptides/ll-37#source-fda-503a)[17](https://www.vitalsvault.com/peptides/ll-37#source-ncpa) ## What this means for you LL-37 is a real and important part of your defenses, an antibiotic your own skin and immune cells make, wired to vitamin D in a way only primates share. As a drug it has two small wound trials, one promising and one that missed its target, and a list of safety questions for anything beyond a gel. If immune defense is your goal, start with the lever you already have. Is your vitamin D level giving your own cells what they need to make LL-37?[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005)[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks) Know your baseline before any peptide 120+ lab tests at Quest Diagnostics, every result reviewed by a licensed clinician. Most results in 3–5 business days. A baseline today gives your clinician something to compare against if you start LL-37 later. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans)[Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist) Full refund before your blood draw · No membership ## What to expect with LL-37 For most people, an LL-37 conversation is really a conversation about vitamin D, skin health and inflammation. A clinician would review your history, check your vitamin D and inflammatory markers, and correct what is low before anything else. The wound trials give the clearest human timing data. In the first trial, healing differences appeared over four weeks of treatment on a gel, with a four-week follow-up. That says nothing about the injections sold online, which have no tested human timeline.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005) ## Key LL-37 studies - Johansson et al., 1998[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998) Lab study · Bacteria and human cells Helical shape tracked antibacterial activity; toxic to human cells at higher levels, inhibited by serum Limits: Lab conditions only - Gombart et al., 2005[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005) Lab and genome study · Human immune, skin and colon cells; mouse cells Vitamin D directly switches on the cathelicidin gene through a primate-only element Limits: Cells, not people - Liu et al., 2006[3](https://www.vitalsvault.com/peptides/ll-37#source-liu-2006) Lab study · Human macrophages and donor blood Immune sensors trigger vitamin D-driven cathelicidin that kills tuberculosis bacteria Limits: Cells, not clinical outcomes - Lande et al., 2007[5](https://www.vitalsvault.com/peptides/ll-37#source-lande-2007) Lab study · Psoriatic skin and immune cells LL-37 turns self-DNA into an interferon trigger in psoriasis Limits: Mechanism, not treatment - Grönberg et al., 2014[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014) Randomized, placebo-controlled, first-in-human · 34 people with venous leg ulcers Lowest strength significantly sped healing; middle strength not significant; highest no advantage Limits: Small; four weeks of treatment - Mahlapuu et al., 2021[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) Phase 2b, randomized, double-blind · 148 people with venous leg ulcers No overall benefit; post hoc signal in large ulcers Limits: Subgroup finding needs a new trial; developer-run Key studies on LL-37 | Study | Design | Who | What it found | Limits | | --- | --- | --- | --- | --- | | Johansson et al., 1998[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998) | Lab study | Bacteria and human cells | Helical shape tracked antibacterial activity; toxic to human cells at higher levels, inhibited by serum | Lab conditions only | | Gombart et al., 2005[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005) | Lab and genome study | Human immune, skin and colon cells; mouse cells | Vitamin D directly switches on the cathelicidin gene through a primate-only element | Cells, not people | | Liu et al., 2006[3](https://www.vitalsvault.com/peptides/ll-37#source-liu-2006) | Lab study | Human macrophages and donor blood | Immune sensors trigger vitamin D-driven cathelicidin that kills tuberculosis bacteria | Cells, not clinical outcomes | | Lande et al., 2007[5](https://www.vitalsvault.com/peptides/ll-37#source-lande-2007) | Lab study | Psoriatic skin and immune cells | LL-37 turns self-DNA into an interferon trigger in psoriasis | Mechanism, not treatment | | Grönberg et al., 2014[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014) | Randomized, placebo-controlled, first-in-human | 34 people with venous leg ulcers | Lowest strength significantly sped healing; middle strength not significant; highest no advantage | Small; four weeks of treatment | | Mahlapuu et al., 2021[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) | Phase 2b, randomized, double-blind | 148 people with venous leg ulcers | No overall benefit; post hoc signal in large ulcers | Subgroup finding needs a new trial; developer-run | ## LL-37 myths and evidence - ### LL-37 injections are proven to heal wounds and the gut The wound trials applied LL-37 to the skin. The first leg ulcer trial was promising at the lowest strength, the larger one found no significant overall benefit, and a diabetic foot ulcer cream trial reported faster healing. No study cited here tested injected LL-37 for wounds or the gut.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[10](https://www.vitalsvault.com/peptides/ll-37#source-miranda-2023) - ### More LL-37 means stronger immunity In the first wound trial the highest strength showed no detectable advantage over placebo, lab studies show it harms human cells at higher levels, and excess LL-37 is implicated in psoriasis and rosacea.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998)[5](https://www.vitalsvault.com/peptides/ll-37#source-lande-2007)[14](https://www.vitalsvault.com/peptides/ll-37#source-coda-2013) - ### LL-37 fights cancer It depends on the tissue, and the evidence is experimental. In lab and animal models, high LL-37 promoted ovarian, lung and breast cancers and suppressed colon and gastric cancers, and FDA notes possible tumor promotion in some tissues.[7](https://www.vitalsvault.com/peptides/ll-37#source-piktel-2016)[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks) - ### You have to take LL-37 to get its benefits Your skin and white blood cells make it already, and vitamin D directly switches on its gene in human cells. How much changing your vitamin D status changes your own LL-37 has not been measured in the studies cited here.[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005)[3](https://www.vitalsvault.com/peptides/ll-37#source-liu-2006) Know your baseline first 120+ lab tests at Quest, every result reviewed by a licensed clinician. Most results in 3–5 business days. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) ## How is LL-37 taken? In trials, LL-37 was applied directly to venous leg ulcers as a gel under a clinical protocol. Online sellers promote injection, but the trials cited here did not test it, and FDA says it lacks the safety information to know whether it would cause harm.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks) ## LL-37 dosage There is no FDA-approved LL-37 dose or route. Wound trials applied an LL-37 solution or cream directly to the ulcer twice a week, and those strengths do not translate to injections. A clinician would not set an injected dose of LL-37 the way they would for an approved medicine.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014)[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021)[10](https://www.vitalsvault.com/peptides/ll-37#source-miranda-2023) ## Typical LL-37 dosage No LL-37 dose is approved. The human doses in this table come from topical wound trials: studies in venous leg ulcers and diabetic foot ulcers applied an LL-37 solution or cream to the wound twice a week for four to thirteen weeks. The only injected use reported in people, an early trial of injection directly into melanoma tumors, does not set a dose for other uses. There is no evidence-based injected dose, and a clinician decides any use. These are reference doses from FDA labels, studies in people and clinical practice reports, shown for education. They are not a recommendation or a prescription. Your dose, form and schedule should be set by a licensed clinician who knows your history and lab results. Already have a prescribed dose? The [peptide dosage calculator](https://www.vitalsvault.com/peptides/tools/dosage-calculator) turns it into the units to draw on an insulin syringe. - Human trial · Applied to the ulcer 0.5, 1.6 or 3.2 mg/mL tested Twice weekly for 4 weeks[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014) Adults with hard-to-heal venous leg ulcers. Healing-rate estimates were higher at both lower strengths, but only 0.5 mg/mL was significantly better than placebo; 3.2 mg/mL showed no difference. - Human trial · Applied to the ulcer 0.5 or 1.6 mg/mL Twice weekly for 13 weeks[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) Phase IIb trial in 148 adults with venous leg ulcers, alongside compression therapy; no overall benefit over placebo. - Human trial · Cream applied to the ulcer 0.5 mg/g cream Twice weekly for 4 weeks[10](https://www.vitalsvault.com/peptides/ll-37#source-miranda-2023) Adults aged 18 to 60 with uninfected or mildly infected diabetic foot ulcers. Typical LL-37 doses in people, by source | Source | Form | Amount | How often | Notes | | --- | --- | --- | --- | --- | | Human trial[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014) | Applied to the ulcer | 0.5, 1.6 or 3.2 mg/mL tested | Twice weekly for 4 weeks | Adults with hard-to-heal venous leg ulcers. Healing-rate estimates were higher at both lower strengths, but only 0.5 mg/mL was significantly better than placebo; 3.2 mg/mL showed no difference. | | Human trial[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) | Applied to the ulcer | 0.5 or 1.6 mg/mL | Twice weekly for 13 weeks | Phase IIb trial in 148 adults with venous leg ulcers, alongside compression therapy; no overall benefit over placebo. | | Human trial[10](https://www.vitalsvault.com/peptides/ll-37#source-miranda-2023) | Cream applied to the ulcer | 0.5 mg/g cream | Twice weekly for 4 weeks | Adults aged 18 to 60 with uninfected or mildly infected diabetic foot ulcers. | ## Is LL-37 right for you? A clinician makes the call. These are the questions they will ask first. ### It may suit - Adults who want to understand how vitamin D and immune defenses relate, with labs to guide it - People with slow-healing leg ulcers who want to know what the trial evidence shows - Anyone who wants a clinician to explain why LL-37 is not a routine option ### Talk to a clinician first if you are - A personal history of cancer, because LL-37 can promote tumor growth in some tissues - Psoriasis, rosacea or another inflammatory skin or autoimmune condition - Pregnant or breastfeeding, or trying to conceive - Allergy or reaction to any peptide product Vitals Vault peptide care starts with a blood panel and a licensed clinician, and ends with a retest. [Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist) ## Vitamin D is the dial for your own LL-37 Your body makes LL-37 on demand. Vitamin D helps switch on its gene in human immune cells, one of the best-described links between a vitamin and an antimicrobial defense. These studies do not show how changing your vitamin D changes your LL-37. More is not always better. LL-37 is high in inflamed skin conditions such as psoriasis, and rosacea has been linked to excess cathelicidin. An injection would turn the dial blindly.[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005)[13](https://www.vitalsvault.com/peptides/ll-37#source-dombrowski-2012)[14](https://www.vitalsvault.com/peptides/ll-37#source-coda-2013) ### What else moves the same system 1. 01Check vitamin DVitamin D helps switch on the LL-37 gene in human cells, and a blood level is easy to check. 2. 02Know your skinLL-37 is high in inflamed skin conditions, so skin changes are worth showing a clinician. 3. 03See a dermatologist for chronic skin diseasePsoriasis and rosacea need specialist care, not a defense peptide. 4. 04Track inflammationhs-CRP is a general, nonspecific marker of inflammation, not a measure of LL-37. ## Labs to check with LL-37 A blood test before you start and a retest after shows what actually changed for you. It is how Vitals Vault approaches every treatment. 1. TestA baseline panel at Quest Diagnostics. 2. DecideA licensed clinician reviews your history and results. 3. RetestThe same markers again, side by side. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) - [Vitamin D (25-OH)Vitamin D switches on the gene that makes LL-37, so your level shapes how much your own cells produce.](https://www.vitalsvault.com/biomarkers/vitamin-d-25-oh-total) - [hs-CRPA blood marker of inflammation you can track before and after a course.](https://www.vitalsvault.com/biomarkers/hs-crp) - [White blood cell countA basic read on your circulating immune cells.](https://www.vitalsvault.com/biomarkers/wbc) - [ZincGeneral immune-health context a clinician may check; it is not an LL-37 test.](https://www.vitalsvault.com/biomarkers/zinc) ## Is LL-37 FDA approved? No. LL-37 is not FDA-approved. FDA’s compounding safety page lists cathelicidin LL-37 among substances previously in category 2 whose nominations were withdrawn, and still describes immunogenicity risk and a lack of safety information, and noting nonclinical findings of effects on male reproduction and possible tumor promotion in some tissues. It is not among the six peptides covered by FDA’s October 2026 enforcement discretion.[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks)[16](https://www.vitalsvault.com/peptides/ll-37#source-fda-503a)[17](https://www.vitalsvault.com/peptides/ll-37#source-ncpa) ### LL-37 timeline 1. 1998 Researchers link LL-37’s helical shape to its antibacterial activity.[1](https://www.vitalsvault.com/peptides/ll-37#source-johansson-1998) 2. 2005 Vitamin D is shown to directly switch on the human cathelicidin gene, through a regulatory element found only in primates.[2](https://www.vitalsvault.com/peptides/ll-37#source-gombart-2005) 3. 2006 Science study links immune sensors, vitamin D and cathelicidin in killing tuberculosis bacteria inside human cells.[3](https://www.vitalsvault.com/peptides/ll-37#source-liu-2006) 4. 2007 Nature study shows LL-37 turns the body’s own DNA into an immune trigger in psoriasis.[5](https://www.vitalsvault.com/peptides/ll-37#source-lande-2007) 5. 2014 First-in-human trial of topical LL-37 in venous leg ulcers reports faster healing at the lowest strength.[8](https://www.vitalsvault.com/peptides/ll-37#source-gronberg-2014) 6. 2021 Phase 2b trial of 148 people finds no overall benefit, with a signal in large ulcers.[9](https://www.vitalsvault.com/peptides/ll-37#source-mahlapuu-2021) 7. April 2026 FDA’s compounding safety page lists cathelicidin LL-37 among withdrawn category 2 nominations, with safety risks noted.[15](https://www.vitalsvault.com/peptides/ll-37#source-fda-bulks) 8. October 29, 2026 FDA grants enforcement discretion to six other peptides, which do not include LL-37.[17](https://www.vitalsvault.com/peptides/ll-37#source-ncpa) ![A Middle Eastern woman, 31, slender, long wavy chestnut hair, hoop earrings listens on a stone terrace](https://www.vitalsvault.com/_next/image?url=%2Fpublic-v3%2Fshoot%2Fpeptides%2Ffaq-ll37.webp&w=3840&q=75&dpl=shadow-production-f0162cb4d465-40992538108-1) ## LL-37 questions What is LL-37 used for? LL-37 is the human cathelicidin antimicrobial peptide. It is studied for chronic wound healing and for its role in defense against infection and in skin inflammation. It is not approved to treat any condition. What are the benefits of LL-37? In a first-in-human trial a topical LL-37 gel sped leg ulcer healing at the lowest strength, but a larger trial found no significant overall benefit. A 2023 trial of an LL-37 cream reported faster diabetic foot ulcer healing. None of these tested the injections sold online. How does LL-37 work? It folds into a helix that disrupts microbes, and it signals to immune cells to direct inflammation and repair. Vitamin D increases how much of it your cells make. What are the side effects of LL-37? Topical LL-37 was well tolerated in leg ulcer trials. FDA notes risks of immunogenicity and impurities, and nonclinical findings of effects on male reproduction and possible tumor promotion in some tissues. Does LL-37 cause cancer? Research is mixed and depends on the tissue. Reviews link high LL-37 to growth of ovarian, lung and breast cancers and to suppression of colon and gastric cancers. FDA says it can be protumorigenic in some tissues. People with a cancer history should talk to a clinician first. Does vitamin D raise LL-37? Yes. Active vitamin D binds a response element in the cathelicidin gene and strongly raises its expression in human immune cells. Blood with low vitamin D supported cathelicidin production poorly in lab studies. What is the LL-37 dosage? There is no FDA-approved dose or route. Wound trials applied LL-37 to the ulcer twice a week, and the one injected use reported in people was an early cancer trial, so there is no evidence-based injected dose. A clinician decides any use. What is the difference between LL-37 and BPC-157? LL-37 is a natural human antimicrobial peptide studied as a gel for chronic wounds. BPC-157 is a stomach-derived peptide studied mainly in animals for tendon and gut repair. They work in different ways. Is LL-37 FDA approved? No. FDA lists cathelicidin LL-37 among bulk substances previously in category 2 whose nominations were withdrawn, and still describes possible safety risks. Withdrawal is not approval, and LL-37 is not covered by the interim policy for category 1 substances. Is LL-37 legal in the US? FDA’s October 2026 enforcement discretion covers six peptides and does not include LL-37. Vials sold online as research use only are not made for people. Can I get LL-37 through Vitals Vault? Vitals Vault is opening clinician-led peptide care that starts with a blood test. Join the peptides waitlist to hear first. LL-37 is not among the peptides covered by FDA’s October 2026 enforcement discretion, so a clinician would start with your vitamin D and inflammation labs. ## Peptides, prescribed and measured Vitals Vault is opening peptide care that starts with your blood work, is prescribed by licensed US clinicians and ends with a retest. Join the waitlist to hear first. - Prescription only - Licensed US clinicians - Quest Diagnostics labs [Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist)[Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) ## Keep reading [Full Peptide Guide](https://www.vitalsvault.com/peptides) - Thymosin alpha-1A 28-amino-acid thymus peptide approved abroad for hepatitis B and C and studied as a vaccine adjuvant and in sepsis. - ThymulinA nine-amino-acid thymus hormone that needs zinc to work, studied for T cell function, inflammation and aging. - KPVA three-amino-acid piece of the hormone alpha-MSH, studied for calming gut and skin inflammation. - FDA peptide update 2026What FDA’s October 2026 decision on six peptides means for you. ## Sources 1. 1. [Johansson J, et al. Conformation-dependent antibacterial activity of the naturally occurring human peptide LL-37. J Biol Chem. 1998 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/9452503/) 2. 2. [Gombart AF, et al. Human cathelicidin antimicrobial peptide (CAMP) gene is a direct target of the vitamin D receptor and is strongly up-regulated in myeloid cells by 1,25-dihydroxyvitamin D3. FASEB J. 2005 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/15985530/) 3. 3. [Liu PT, et al. Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response. Science. 2006 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/16497887/) 4. 4. [Martineau AR, et al. IFN-gamma- and TNF-independent vitamin D-inducible human suppression of mycobacteria: the role of cathelicidin LL-37. J Immunol. 2007 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/17513768/) 5. 5. [Lande R, et al. Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide. Nature. 2007 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/17873860/) 6. 6. [Fabisiak A, et al. LL-37: Cathelicidin-related antimicrobial peptide with pleiotropic activity. Pharmacol Rep. 2016 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/27117377/) 7. 7. [Piktel E, et al. The Role of Cathelicidin LL-37 in Cancer Development. Arch Immunol Ther Exp (Warsz). 2016 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/26395996/) 8. 8. [Grönberg A, et al. 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 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/25041740/) 9. 9. [Mahlapuu M, 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 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/34687253/) 10. 10. [Miranda E, et al. Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trial. Arch Dermatol Res. 2023 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/37480520/) 11. 11. [Dolkar T, et al. Dermatologic toxicity from novel therapy using antimicrobial peptide LL-37 in melanoma: a detailed examination of the clinicopathologic features. J Cutan Pathol. 2018 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/29665030/) 12. 12. [Zhao Y, et al. Efficacy and safety of Oral LL-37 against the Omicron BA.5.1.3 variant of SARS-COV-2: a randomized trial. J Med Virol. 2023 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/37605995/) 13. 13. [Dombrowski Y, et al. Cathelicidin LL-37: a defense molecule with a potential role in psoriasis pathogenesis. Exp Dermatol. 2012 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/22509827/) 14. 14. [Coda AB, et al. Cathelicidin, kallikrein 5, and serine protease activity is inhibited during treatment of rosacea with azelaic acid 15% gel. J Am Acad Dermatol. 2013 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/23871720/) 15. 15. [FDA. Certain bulk drug substances for use in compounding that may present significant safety risks (current as of April 22, 2026) (opens in a new tab)](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks) 16. 16. [FDA. Bulk drug substances used in compounding under section 503A (opens in a new tab)](https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act) 17. 17. [NCPA. FDA grants enforcement discretion for compounding six peptides. October 29, 2026 (opens in a new tab)](https://ncpa.org/newsroom/qam/2026/10/29/fda-grants-enforcement-discretion-compounding-six-peptides) Written by the Vitals Vault editorial team, medically reviewed by Robert Lufkin, MD, and updated October 29, 2026. This is general education, not medical advice. None of these peptides is FDA-approved to diagnose, treat, cure or prevent any disease, and compounded medicines are not FDA-reviewed for safety, effectiveness or quality. Talk to a licensed clinician before starting any treatment. --- Canonical HTML: https://www.vitalsvault.com/peptides/ll-37 - [llms.txt](https://www.vitalsvault.com/llms.txt) - [sitemap.xml](https://www.vitalsvault.com/sitemap.xml) - [Developer portal](https://www.vitalsvault.com/developers)