What isLL-37FDA Status, Evidence and Risks (2026)

What LL-37 is

LL-37 is a peptide your own body makes. It is 37 amino acids long and starts with two leucines, L and L ⁵.

It is the only member of the cathelicidin family made in humans, from a single gene called CAMP ⁵. The body stores it as a bigger protein, hCAP18, mostly in neutrophils, a type of white blood cell. An enzyme cuts LL-37 free when it's needed ⁵.

It shows up in sweat, semen, urine, breast milk and blood plasma ⁵. In lab research it kills microbes, signals the immune system, helps grow blood vessels and plays a part in wound repair ⁵.

As a drug, it has problems. A 2022 review lists poor bioavailability, high production cost and possible toxicity to cells. Enzymes in the gut and blood break it down fast. Part of the molecule has been tied to hemolysis, the bursting of red blood cells ⁵.

Where FDA stands

1. Before Apr 2026: on FDA's Category 2 list, the bulk substances FDA says "may present significant safety risks" in compounding ¹.
2. Apr 15, 2026: FDA said it would remove 12 peptides, LL-37 among them, "within seven calendar days," because their nominators withdrew them ³.
3. Apr 22, 2026: FDA's page now lists LL-37 in its withdrawn table, with its safety concerns still attached ¹.
4. Before end of Feb 2027: FDA's Pharmacy Compounding Advisory Committee is expected to review LL-37, with injectable GHK-Cu, dihexa, melanotan II and PEG-MGF. No date is set ⁴. Any vote would be advice only.
5. Today: not approved by FDA for any use and not on the 503A bulks list ². Coming off Category 2 approved nothing. Are Peptides Legal? explains why.

Not in the HHS policy. On Oct 28, 2026, HHS filed an interim enforcement discretion policy covering six peptides: BPC-157, TB-500, MOTS-c, epitalon, semax and KPV ¹⁰. LL-37 is not one of them and keeps its prior status, as of Oct 29, 2026. The FDA Peptide Tracker logs every change, and HHS's Oct 28 peptide policy has the full breakdown.

What the research shows

We found no country where LL-37 is an approved drug. Human data comes from a few small trials. Most of the rest is lab and animal work.

Leg ulcers, first trial (2014). 34 people with hard-to-heal venous leg ulcers. LL-37 was applied to the wound twice a week for 4 weeks at three strengths, or a placebo ⁷. The authors reported better healing with the two lower strengths and no safety concerns. The highest strength did no better than placebo ⁷. Small and short.

Leg ulcers, the bigger trial (Phase 2b, 2018 to 2020). This is the one that counts. EU trial 2018-000536-10, run by Promore Pharma, mostly in Poland ⁸:

Everyone also got standard ulcer care and compression bandages, for up to 13 weeks ⁸. Neither strength beat placebo on full closure. Healing rate and time to closure showed no significant difference either ⁸. In the higher-strength group, 4 people stopped treatment because of adverse events ⁸.

Melanoma (2015 to 2020). A Phase 1/2 study at MD Anderson injected LL-37 into melanoma tumors on the skin. It enrolled 4 people and is listed as completed ⁹. Four people cannot tell anyone whether it works.

Infections. LL-37 kills microbes in lab research ⁵. We found no completed trial showing LL-37 treats an infection in people.

Side effects and FDA's concerns

FDA's stated concerns, from its Category 2 page ¹:

• Immune reactions. Compounded LL-37 "may pose risk for immunogenicity for certain routes of administration."
• Impurities. Complexities with peptide-related impurities and characterizing the ingredient.
• Not enough safety data. FDA "lacks sufficient safety-related information" to know whether it would harm people.
• Male reproduction. "Nonclinical research findings suggest detrimental effects on male reproduction." Nonclinical means lab or animal studies.
• Tumors. FDA says it "can be protumorigenic in some tissues," meaning it may help some tumors grow.

The tumor question is messy in the research too. Reviews describe LL-37 pushing growth of breast, lung, prostate and ovarian cancer cells in lab studies, and slowing gastric and colon cancer cells ^5,6. LL-37 is found at higher levels in ovarian cancers than in normal ovarian tissue ⁶. A 2022 review lists melanoma among the cancers it can promote ⁵. The authors of both reviews say no one has explained the opposite effects ^5,6.

Other flags from the research: possible toxicity to cells and a link to bursting red blood cells ⁵.

Why it's sold online anyway

LL-37 is easy to find online, often labeled "research use only." That label is the seller saying the product is not made for people. Those vials skip a prescriber, a licensed pharmacy and any quality check for human use. FDA's own list flags impurities as a concern for this peptide ¹. Prescription vs Research Peptides has more.

Other peptides on this shelf: KPV, the three-amino-acid gut peptide in HHS's new policy, and PEG-MGF, which waits for the same review as LL-37.

Asked a lot.

The sources.

1. FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of Apr 22, 2026). Read it
2. FDA. Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act (content current as of May 14, 2026). Read it
3. Frier Levitt. FDA Peptides "Do Not Compound" List Update (Apr 16, 2026). Read it
4. Holland & Knight. Peptides at a Crossroads: What Wellness Providers Need to Know (Oct 16, 2026). Read it
5. Lu F, Zhu Y, Zhang G, Liu Z. Renovation as innovation: repurposing human antibacterial peptide LL-37 for cancer therapy. Front Pharmacol. 2022;13. doi:10.3389/fphar.2022.944147. Read it
6. Kuroda K, Okumura K, Isogai H, Isogai E. The human cathelicidin antimicrobial peptide LL-37 and mimics are potential anticancer drugs. Front Oncol. 2015;5:144. Read it
7. 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. doi:10.1111/wrr.12211. PMID 25041740 (Europe PMC record). Read it
8. EU Clinical Trials Register. EudraCT 2018-000536-10: A Phase IIb, double-blind, randomised, placebo-controlled, multi-centre trial of locally administered LL-37 in patients with hard-to-heal venous leg ulcers. Sponsor Promore Pharma AB. Results first published Jul 26, 2021. Read it
9. ClinicalTrials.gov. NCT02225366: Intratumoral Injections of LL37 for Melanoma. M.D. Anderson Cancer Center (study record). Read it
10. HHS. Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances. Docket HHS-OASH-2026-0496, FR Doc 2026-22192 (filed for public inspection Oct 28, 2026; scheduled to publish in the Federal Register Oct 30, 2026). Read it