LL-37

What is LL-37?

On the first line of defense against microbes, the human body produces short protein fragments called “antimicrobial peptides”. Cathelicidins are a branch of this family. According to a 2018 review, LL-37 is the peptide cleaved from the end portion of the human cathelicidin antimicrobial protein (CAMP, hCAP18); it increases resistance to microbes, recruits immune cells to the site of inflammation, and supports wound closure and new blood vessel formation. The same review also describes that cathelicidin production in human macrophages is increased in a vitamin D-dependent manner. ^[6]

That it is a peptide the body makes itself does not mean that LL-37 given from outside is safe or beneficial. As will be seen below, the same properties of LL-37 also feed inflammation and the autoimmune response in some diseases.

What did human wound-healing studies show?

Human data on LL-37 in wound treatment amount to three randomized studies with products applied to chronic wounds that do not heal.

This table shows that the promising result of the first small study was not replicated in the larger study. In the first study, 34 people were divided into four groups, and at the highest concentration no improvement different from placebo was seen. ^[1] In the phase 2b study, the mean wound size at randomization was 11.6 cm². ^[2] The authors of the HEAL LL-37 study write that the possible benefit in large ulcers can only be tested with a new study adequately powered for this patient group. ^[2] The diabetic foot study was done with only 25 patients and measured intermediate indicators such as granulation tissue instead of complete closure. ^[3] In all three studies, LL-37 was applied to the wound; the results cannot be carried over to injection or oral use.

What are injection and general-use claims based on?

That LL-37 has been prepared and sold for human use is also in official records: in a 2020 warning letter, the FDA found that a compounding pharmacy was preparing drugs with numerous peptides, including LL-37, that are not on the list of bulk substances pharmacies may use and had not been nominated, and that products that must be sterile were prepared under unhygienic conditions, that is, may have been contaminated. ^[10] None of the three studies above examined use by injection. According to the FDA’s assessment dated April 22, 2026, the FDA does not have enough safety information to know whether LL-37 would harm humans when given to them. ^[8]

The published human experience in which LL-37 was given by injection is from the cancer field: in the US, LL-37 was injected directly into tumors in melanoma patients with skin metastases. In a case report published from this study, in a 63-year-old woman who had not responded to previous treatments, the treated lesions shrank during 8 weeks of injections; however, about 45 days after treatment started, numerous wart-like eruptions and a blistering lesion, at first glance suggesting skin cancer or inflamed keratosis, developed on the trunk and arms. Biopsies showed dense inflammation with atypical cell proliferation; the lesions regressed within 2 months after treatment was stopped. ^[7] This single case is not safety data for use in healthy people; it only shows that the peptide can provoke strong immune reactions in the skin.

What is the relationship with autoimmune diseases and cancer?

Against claims presenting LL-37 as a “harmless, natural peptide”, there are laboratory and patient-sample studies showing it in the mechanism of autoimmune diseases. These studies examine the LL-37 the body makes itself and do not show that LL-37 given from outside starts autoimmune disease. What they show is the side of LL-37 that feeds inflammation and the autoimmune response in these diseases.

Psoriasis

Plasmacytoid dendritic cells in the immune system normally do not react to the body’s own DNA. A study published in 2007 showed that in psoriasis, LL-37 binds the body’s own DNA released from damaged cells and forms dense clusters, and that these clusters trigger strong interferon production in dendritic cells. According to the authors, this pathway can sustain autoimmunity in psoriasis by breaking natural tolerance to one’s own DNA. ^[4]

Lupus

In the blood of patients with systemic lupus erythematosus, complexes formed from antimicrobial peptides coming from web-like structures released by neutrophils (NETs) and the person’s own DNA were detected; these activated dendritic cells. Patients had developed autoantibodies against both DNA and these peptides, and the neutrophils of lupus patients released more NETs than those of healthy people. ^[5] Two authors of this study hold a patent on substances that block the LL-37-mediated immune response. ^[5]

Cancer

According to the 2018 review, LL-37 shows tumor-promoting effects in ovarian, lung, breast, prostate and pancreatic cancers and in melanoma and squamous cell carcinoma of the skin, while it shows anticancer effects in colon, stomach and blood cancers and in oral squamous cell carcinoma; the effect varies by tissue. ^[6] The FDA also writes that nonclinical findings suggest that LL-37 may promote tumor formation in some tissues and may have harmful effects on male reproductive health. ^[8] These findings rest on laboratory and animal studies; the relationship between externally given LL-37 and cancer has not been examined in humans.

Legal status: FDA, WADA and Türkiye

US: category 2 and the advisory committee

The FDA places substances nominated for use in drugs prepared in pharmacies (compounded) that may present significant safety risks in “category 2”. LL-37 was in this category. On the FDA page dated April 22, 2026, “cathelicidin LL-37” has been moved to the table of substances whose nomination was withdrawn by the nominators. The FDA’s reasoning in the same row: compounded drugs containing LL-37 may carry a risk of immune response with some routes of administration, peptide-related impurities and characterization of the bulk substance may be complex, safety information in humans is insufficient, and nonclinical findings suggest harm to male reproductive health and the possibility of promoting tumor formation in some tissues. ^[8]

According to the FDA’s announcement dated April 15, 2026, the Pharmacy Compounding Advisory Committee (PCAC) will consider cathelicidin LL-37, together with GHK-Cu, dihexa acetate, Melanotan II and PEG-MGF, at a meeting to be held before the end of February 2027, on whether to add them to the list of bulk substances pharmacies may use. Advisory committees give non-binding recommendations. ^[9] This process is not a drug approval. The meaning of the “for research purposes” label: What does research peptide mean?

Sport (WADA)

The WADA list valid from January 1, 2026 does not name LL-37. Class S0 prohibits at all times (in and out of competition) pharmacological substances that are not covered in another section of the list and are not approved by any official health authority for therapeutic use in humans; drugs in clinical development are given as an example of this definition, and the class is defined with examples “including but not limited to”. ^[11] The most advanced wound study published with LL-37 is at phase 2b ^[2] and it has no licensed product on the TİTCK list; the classification of a specific substance is within WADA’s authority.

Türkiye

The TİTCK (Turkish Medicines and Medical Devices Agency) Licensed Human Medicinal Products List dated October 16, 2026 contains no product with LL-37 (cathelicidin) as an active substance. ^[12] Article 19 of Law No. 1262 (İspençiyari ve Tıbbi Müstahzarlar Kanunu) punishes those who manufacture unlicensed preparations and those who knowingly sell, offer for sale or have sold them with imprisonment from one to five years; the same penalty is prescribed for those who sell, market or advertise a product that is not a preparation with the claim that it diagnoses or treats diseases. Importing preparations made abroad without a license for commercial purposes counts as smuggling. ^[13] Under Article 24 of Law No. 6197, medicines cannot be sold on the internet or in any other electronic medium. ^[14]

General legal framework of peptides: Are peptides legal? · General risks: Peptide side effects

Evidence table: claim, population and limits

Limits of this guide

This page summarizes published human studies, mechanism research and official agency assessments on LL-37. It gives no dose, cycle, preparation, administration technique or product-sourcing information. Laboratory and animal findings are not evidence of benefit or safety in humans.