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LL-37

Human cathelicidin antimicrobial peptide

Status

Not approved

Not approved anywhere; FDA listed cathelicidin LL-37 in 503A Category 2 (citing animal signals of harm to male reproduction and tumour promotion) until its nomination was withdrawn in April 2026, and an FDA advisory committee is scheduled to review it by February 2027.

Evidence

Preliminary

Two small randomised trials of topical LL-37 for leg ulcers (the larger one missed its main endpoint) and a 4-patient melanoma study; no human data support injected use.

In sport

WADAProhibited (WADA)

LL-37 is a 37-amino-acid antimicrobial peptide cut from the human protein hCAP18, part of the innate immune defences of neutrophils and skin. It was tested as a topical leg-ulcer treatment without clear success and is sold as a research chemical.

Structure

37 residues

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Sequence as text
H-L-L-G-D-F-F-R-K-S-K-E-K-I-G-K-E-F-K-R-I-V-Q-R-I-K-D-F-L-R-N-L-V-P-R-T-E-S-OH

What it is used for

  • Hard-to-heal venous leg ulcers as a topical treatment, in phase 2 trials (studied)
  • Melanoma by injection into tumours, in a 4-patient early trial (studied)
  • Immune support and chronic infections (claimed, unproven)

How it works

LL-37 is part of the innate immune system. It binds bacterial lipopolysaccharide and kills a broad range of bacteria and some fungi in the lab by forming pores in their membranes, and it may disrupt biofilm signalling. It also acts on immune and skin cells: it signals through formyl peptide receptors on neutrophils and makes keratinocytes release cytokines and chemokines. In lab tests it can also damage red blood cells.

How strong the evidence is

PreliminarySmall human studies, pilots or observational data.

In a placebo-controlled phase 1/2 trial of 34 patients with venous leg ulcers (Grönberg 2014), topical LL-37 gave healing rates several times higher than placebo. The larger phase 2b HEAL LL-37 trial (Mahlapuu 2021; 144 patients, 13 weeks) missed its primary endpoint: complete closure in 26.5% and 24.7% on two doses versus 25.3% on placebo, with benefit only in a post hoc analysis of ulcers of 10 cm2 or more. An MD Anderson trial injecting LL-37 into melanoma (NCT02225366) enrolled 4 patients. No trials support injected use for immune or infection claims.

Risks and side effects

  • FDA judged safety information insufficient and noted animal findings of harm to male reproduction and tumour-promoting effects in some tissues.
  • Local wound-site reactions were reported in roughly 40% of participants across the arms of the phase 2b trial, mostly mild to moderate.
  • Research-chemical products carry impurity and immune-reaction (immunogenicity) risks, according to FDA.
  • Not named by WADA but, as an unapproved pharmacological substance, falls under the S0 class, whose 2027 wording lists peptides explicitly.

Regulatory status

No regulator has approved this peptide for any use.

Status by country

JurisdictionStatusSource
USUnited StatesNo authorised medicineSource 3
EUEuropean UnionNo authorised medicineSource 10
UKUnited KingdomNo authorised medicineSource 11
AUAustraliaNo authorised medicineSource 12
CACanadaNo authorised medicineSource 13
Whether a medicine containing it is authorised, checked in each regulator’s records on Oct 1, 2026.

Status of every peptide by country

Timeline

  1. 2026

    1. RegulatoryFDA removes BPC-157 and 11 other peptides from its compounding safety-risk list

Sources

  1. 01UniProtKB P49913: Cathelicidin antimicrobial peptide (CAMP), human(opens the source in a new tab) UniProt, 2026
  2. 02PubChem Compound Summary: LL-37 (CID 16198951)(opens the source in a new tab) NCBI PubChem, 2026
  3. 03Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks(opens the source in a new tab) US Food and Drug Administration, 2026
  4. 04Meeting of the Pharmacy Compounding Advisory Committee (before end of February 2027)(opens the source in a new tab) US Food and Drug Administration, 2026
  5. 05Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial(opens the source in a new tab) Wound Repair and Regeneration, 2014
  6. 06Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trial(opens the source in a new tab) Wound Repair and Regeneration, 2021
  7. 07Intratumoral Injections of LL37 for Melanoma (NCT02225366)(opens the source in a new tab) ClinicalTrials.gov, 2020
  8. 08World Anti-Doping Code International Standard: Prohibited List 2026(opens the source in a new tab) World Anti-Doping Agency, 2025
  9. 09WADA publishes 2027 Prohibited List(opens the source in a new tab) World Anti-Doping Agency, 2026
  10. 10Find medicine: centrally authorised medicines(opens the source in a new tab) European Medicines Agency, 2026
  11. 11MHRA Products: active substances beginning with L(opens the source in a new tab) Medicines and Healthcare products Regulatory Agency, 2026
  12. 12Australian Register of Therapeutic Goods (ARTG)(opens the source in a new tab) Therapeutic Goods Administration
  13. 13Unauthorized injectable peptide drugs seized and sold by Canada Peptide may pose serious health risks(opens the source in a new tab) Health Canada, 2025
  1. Approved elsewhereThymosin alpha-1Thymic peptide immunomodulator28
  2. Not approvedKPVAlpha-MSH-derived tripeptide (research chemical)3 WADA banned

Educational information, not medical advice. Talk to a licensed clinician before starting, stopping or changing any medicine.