LL-37

CNot approvedcathelicidinhCAP18 fragmentantimicrobial peptide
In one paragraphLL-37 is the only cathelicidin peptide humans make — a 37-amino-acid antimicrobial produced by skin, gut and immune cells that kills bacteria and signals inflammation and repair. The human evidence is two randomised trials of a topical gel on venous leg ulcers: a 34-patient phase 2a that found faster healing, and a 148-patient phase 2b that did not, except in a subgroup of large wounds. Nothing supports the injected 'immune' or 'anti-inflammatory' uses sold online, and injected LL-37 is pro-inflammatory in the laboratory.
Schematic 3D structure of LL-37
37 residues · amphipathic α-helix in membranes · schematic
Overall gradeC Weak
Human trials2 RCTs (topical)
Outcomes graded4
Last reviewed3 September 2026
EvidenceWhat it isHow it worksUnknownsRegulationQuestionsReferences

What the human research shows

C because there are real randomised trials — and they are equivocal. The larger, better trial was negative on its primary endpoint. Everything about systemic use is animal or cell data, and the biology cuts both ways: LL-37 is implicated in psoriasis, rosacea and autoimmunity, not only in defence.

OutcomeGradeEffect sizeHuman studiesWhere the evidence comes from
Venous leg ulcer healing (topical)CWeakSmall2 RCTs (n=34, n=148)Phase 2a (2014): 34 patients, healing rate roughly six-fold faster at 0.5 mg/ml than placebo over 4 weeks. Phase 2b (2021): 148 patients, 13 weeks; complete closure 26.5% and 24.7% versus 25.3% on placebo — no difference overall, a significant benefit only in ulcers of 10 cm² or more (28.1% versus 8.1%).12
Antimicrobial action in peopleDNo human evidenceNot measurable0 controlledKills bacteria in vitro and in animal models; no human trial has tested LL-37 as an anti-infective in any route.3
Systemic 'immune support' or anti-inflammatory useDNo human evidenceNot measurable0No human data by injection at all. In cells and mice LL-37 is a driver of inflammation in psoriasis and lupus, which argues against, not for, the marketed use.3
Safety (topical)adverseCWeakNot measurable2 RCTsTopical gel well tolerated in both trials; serious adverse events in 7.4% of the phase 2b population, none attributed to the drug. Nothing is known about injected use.2
AMultiple good human trials, consistentBSome human trials, mostly consistentCFew or weak human studiesDAnimal or anecdotal onlyeffect size · red = adverse

Literature searched to 3 September 2026. Human studies only; animal and cell work informs the mechanism section and nothing else.

What it is

The active fragment cleaved from the human cathelicidin precursor hCAP18. It is part of innate immunity: released by neutrophils, keratinocytes and epithelial cells, it disrupts bacterial membranes, binds endotoxin and recruits immune cells.

A Swedish company, Pergamum (later Promore Pharma), developed a topical LL-37 gel (LL-37/PXL01 programme) for chronic wounds; the 2021 phase 2b result stalled it. No systemic LL-37 product has ever entered a human trial.

How it is thought to work

Its amphipathic helix inserts into bacterial membranes. Separately it acts on host receptors — FPR2, P2X7, EGFR — to drive chemotaxis, angiogenesis and re-epithelialisation, which is the wound-healing rationale. The same signalling, sustained, is a feature of inflammatory skin disease.

What is still unknown

  • Whether a topical product could work in a defined wound population — the phase 2b subgroup was not pre-specified.
  • Anything at all about injected LL-37 in humans.

Regulatory status

European Union
Unauthorised medicinal product

No marketing authorisation. Supplying it for human use is an offence under national medicines law.

United States
Not approved; compounding withdrawn

Its 503A nomination (cathelicidin LL-37) is listed as withdrawn since April 2026; it was not among the peptides the advisory committee reviewed in July 2026.

United Kingdom
Unlicensed medicine

Selling or supplying it for human use is an offence.

Australia
Schedule 4, unapproved

Prescription-only substance not on the ARTG.

Canada
Not authorised

No DIN; selling it is illegal.

Sport (WADA)
Prohibited at all times

Unapproved anywhere, so it falls under S0 (non-approved substances).

Questions people actually ask

Does LL-37 heal wounds?
In the larger of two randomised trials, no better than placebo overall: complete closure in about a quarter of patients in every group after 13 weeks. Large ulcers did better on the low dose in a subgroup analysis. The small earlier trial was positive.
Is LL-37 an antibiotic?
In the test tube, yes — it is part of the body's own antimicrobial defence. No human trial has tested it as an anti-infective, and it degrades quickly in blood.
Is injected LL-37 anti-inflammatory?
The laboratory evidence points the other way: LL-37 drives inflammation in psoriasis and lupus models. There are no human data for injected use in any condition.

One page per claimed effect

References

  1. 1
  2. 2
  3. 3
    Reviews of LL-37 biology in infection, wound repair and autoimmunity.VariousPreclinical mechanism; no systemic human data.

Change log

  • 2026-09-03Initial publication from the two topical wound-healing trials.