Is LL-37 FDA-approved, and what does the research show?

What is LL-37?

LL-37 is an antimicrobial peptide, a short chain of amino acids that the body uses against microbes ¹. It is the only member of the cathelicidin family, a group of antimicrobial peptides, that humans make ¹. The body produces a larger precursor protein, hCAP18, and cuts the active 37-amino-acid peptide from it ², ³. White blood cells called neutrophils and the cells lining the skin and other surfaces are its main sources ¹. The LL-37 in the wound trials is a synthetic copy of this natural molecule ⁹.

Is LL-37 FDA-approved?

LL-37 is not FDA-approved: Drugs@FDA lists no approved LL-37 product as of November 9, 2026 ⁴. It is a research compound tested in people in small and mid-sized trials, none of which has led to an approved drug ⁸, ⁹, ¹⁰, ¹².

LL-37 is not named in any category on FDA's list of bulk drug substances nominated for compounding under section 503A, updated May 14, 2026 ⁵. Compounding is a licensed pharmacist or physician making a medicine for one patient on a prescription, and section 503A is the part of federal law that sets its conditions ¹³. It is not named on the 503B list for outsourcing facilities, updated March 21, 2025 ⁶.

FDA added "Cathelicidin LL-37" to 503A Category 2 on September 29, 2023, the date its safety-risks page gave for the addition ¹⁴. By September 2024 the 503A list showed it under the heading "503A Category 2: Bulk Drug Substances that Raise Significant Safety Risks" ¹⁵. FDA's safety-risks page, current as of April 22, 2026, now lists it under the heading "Bulk drug substances nominated but withdrawn" ⁷. That heading covers substances "previously in category 2 of the interim policies" that "were withdrawn by the nominators" ⁷. The page's version captured on April 21, 2026, still showed LL-37 in Category 2, so the withdrawal appeared on FDA's page between that capture and April 22, 2026 ¹⁴, ⁷.

For a reader, that means no FDA document opened for this page describes a lawful route to compounded LL-37 ⁵, ⁶, ⁷, ¹³. FDA's warning letter of November 10, 2021, to an Indiana clinic listed LL-37 among eight substances that "were not nominated for inclusion on the 503A bulks list" ¹³. The same letter explains the rule it applied ¹³. A drug compounded from a substance with no USP monograph, an official quality standard, not in an approved drug and not on the 503A list is "not eligible for the exemptions provided by section 503A(a)" ¹³. One of those exemptions is from the requirement for FDA approval before marketing ¹³.

See the FDA status of every peptide, updated weekly.

How does LL-37 work?

LL-37 carries a positive charge ¹⁶ and binds to the outer surface of bacteria, breaking open their membranes ¹⁷. Shown with purified peptide in the laboratory, it stopped the growth of a range of bacteria, including Pseudomonas aeruginosa and Staphylococcus aureus, and bound the endotoxin that bacteria shed ¹⁷. It also binds siderophores, the iron-scavenging molecules bacteria release to feed themselves, shown with purified peptide in 2020 ¹⁶. In human monocytes, a type of white blood cell, in culture it damped the inflammatory signals set off by bacterial endotoxin ¹⁸. Trial authors proposed that these actions, with effects on blood-vessel growth and skin-cell movement, might speed the closing of chronic wounds; that hypothesis is what the ulcer trials tested ¹⁰, ⁹.

What does the research show?

Venous leg ulcers. A first-in-man randomized trial in Sweden studied 34 people with hard-to-heal venous leg ulcers ⁸. After a three-week run-in, a period on placebo before the trial proper, participants had LL-37 or placebo applied to the ulcer twice a week for four weeks ⁸.

The lowest strength's healing rate was about six times placebo's (p = 0.003, a difference unlikely to be chance) ⁸. The middle strength's was about three times placebo's (p = 0.088), a difference that did not reach statistical significance ⁸. The highest strength did no better than placebo ⁸.

The follow-up trial, HEAL LL-37, was a phase 2b study, a mid-stage trial of effect in patients ⁹. It randomized 149 people with hard-to-heal venous leg ulcers at 15 sites in Poland and Sweden, and treated 148 ⁹. Two strengths of LL-37 or placebo were applied twice a week for 13 weeks alongside compression bandaging ⁹.

Confirmed complete closure was reached by 26.5 percent and 24.7 percent in the two LL-37 groups and 25.3 percent on placebo, no significant difference ⁹. A post hoc analysis, one decided after the results were in, found significant improvement on the lower strength in the subgroup whose ulcers measured at least 10 square centimeters ⁹. The authors call it an observation that needs a trial of its own ⁹.

Diabetic foot ulcers. A randomized, double-blind trial in Jakarta gave 13 people with diabetic foot ulcers LL-37 cream and 12 a placebo cream, twice a week for four weeks ¹⁰. The granulation index, a measure of new wound tissue, rose more in the LL-37 group at each of four weekly measurements (p between 0.006 and 0.037) ¹⁰. Inflammatory markers in wound fluid and bacterial counts did not differ between the groups ¹⁰.

Melanoma. At MD Anderson Cancer Center, a phase 1/2 study, an early test of safety and dose, injected LL-37 directly into skin deposits of metastatic melanoma ¹¹. The injections were given once a week for up to eight weeks ¹¹. Four people enrolled, the posted results cover three, and one left the study for lack of efficacy ¹¹. The posted results report no serious adverse events and no deaths ¹¹; no published report of the trial's results was found in PubMed on November 9, 2026.

COVID-19. In China, an open-label randomized trial gave 238 hospital inpatients with the Omicron BA.5.1.3 variant either placebo or "Oral LL-37", Lactococcus lactis bacteria engineered to make the peptide ¹². The authors report a significantly shorter time to a negative viral test with Oral LL-37 than with placebo ¹². They report no severe adverse events ¹². This single-center study tested a bacterial product that makes LL-37, not the peptide itself ¹².

No published human trial of LL-37 injected under the skin or into a vein was found in PubMed or ClinicalTrials.gov on November 9, 2026. The same searches found no trial of LL-37 for immune support, infection prevention or aging.

What are the side effects?

FDA's safety-risks page says 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" ⁷. API is the active ingredient. FDA "lacks sufficient safety-related information regarding cathelicidin LL-37 to know whether the drug would cause harm when administered to humans" ⁷. It adds that "Nonclinical research findings suggest detrimental effects on male reproduction and that this drug can be protumorigenic in some tissues" ⁷. Immunogenicity means the body may mount an immune reaction against the peptide; protumorigenic means it may encourage tumor growth.

In the 148-person venous leg ulcer trial, local reactions were common in every group ⁹. Redness at the ulcer affected 42.6 percent of participants and scaling of the nearby skin 52.7 percent, mostly mild or moderate ⁹. The trial found no consistent difference in these reactions between LL-37 and placebo ⁹.

There were no deaths; 12 serious adverse events occurred in 11 people (7.4 percent), none judged related to the study drug ⁹. The 34-person trial reported "no safety concerns regarding local or systemic adverse events" ⁸. In the 25-person diabetic foot ulcer trial the authors report no side effect caused by the cream, and no participant withdrew ¹⁰. One of the 13 people on LL-37 had mild irritant contact dermatitis from wound fluid, which resolved with an absorbent dressing ¹⁰.

The melanoma study's posted results list anemia in two of the three treated people ¹¹. In the first group of two, one person each had a second skin cancer (squamous cell carcinoma) and a precancerous sun-damage patch (actinic keratosis) ¹¹. In that group one person each also had a loss of skin color and an underactive thyroid ¹¹. The one person in the second group had falls in two kinds of white-cell count and a rise in bilirubin, a liver test ¹¹. None was classed serious ¹¹.

A 2018 case report describes a 63-year-old woman with stage IIIC melanoma who received eight weekly LL-37 injections into her tumors ³. About 45 days after the injections began she developed multiple wart-like and blistering skin lesions, which resolved within two months of stopping ³. The MD Anderson melanoma trial excluded people with active autoimmune disease needing treatment, those on systemic steroids and those with any immunodeficiency ¹¹.

In sport

LL-37 is not named on the World Anti-Doping Agency's 2026 Prohibited List ¹⁹. Not named is not the same as allowed, because the list opens with a catch-all clause ¹⁹.

The list's S0 clause reads: "Any pharmacological substance which is not addressed by any of the subsequent sections of the List and with no current approval by any governmental regulatory health authority for human therapeutic use (e.g. drugs under pre-clinical or clinical development or discontinued, designer drugs, substances approved only for veterinary use) is prohibited at all times" ¹⁹. FDA, the only regulator whose records were read for this page, lists no approved LL-37 product ⁴. Whether S0 reaches LL-37 is a question for an athlete's anti-doping organization.

What JumpstartMD offers

JumpstartMD does not prescribe LL-37. Our peptide library covers it so you have the facts on its FDA status and the evidence, current as of November 9, 2026.

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Compounded medications are not FDA-approved, and FDA does not review their safety, effectiveness, or quality before they are marketed. A licensed clinician decides after an evaluation whether a peptide is appropriate for you, and not every patient will qualify.