{"id":"ll-37","name":"LL-37","aliases":["cathelicidin","hCAP18 fragment","antimicrobial peptide"],"url":"https://lyoresearch.com/compounds/ll-37","summary":"LL-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.","overall_grade":"C","overall_grade_meaning":"weak human evidence","human_trials":"2 RCTs (topical)","regulatory_status":"Not approved","outcomes":[{"outcome":"Venous leg ulcer healing (topical)","grade":"C","grade_meaning":"weak human evidence","effect_size":"small","adverse":false,"human_studies":"2 RCTs (n=34, n=148)","evidence":"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%).","references":[{"citation":"Grönberg A, et al. Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial.","where":"Wound Repair Regen, 2014; DOI 10.1111/wrr.12211","url":"https://pubmed.ncbi.nlm.nih.gov/25041740/"},{"citation":"Mahlapuu M, et al. Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial.","where":"Wound Repair Regen, 2021","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC9298190/"}]},{"outcome":"Antimicrobial action in people","grade":"D","grade_meaning":"no human evidence","effect_size":"not measurable","adverse":false,"human_studies":"0 controlled","evidence":"Kills bacteria in vitro and in animal models; no human trial has tested LL-37 as an anti-infective in any route.","references":[{"citation":"Reviews of LL-37 biology in infection, wound repair and autoimmunity.","where":"Various","url":"https://pubmed.ncbi.nlm.nih.gov/?term=LL-37+cathelicidin+review+psoriasis+inflammation"}]},{"outcome":"Systemic 'immune support' or anti-inflammatory use","grade":"D","grade_meaning":"no human evidence","effect_size":"not measurable","adverse":false,"human_studies":"0","evidence":"No 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.","references":[{"citation":"Reviews of LL-37 biology in infection, wound repair and autoimmunity.","where":"Various","url":"https://pubmed.ncbi.nlm.nih.gov/?term=LL-37+cathelicidin+review+psoriasis+inflammation"}]},{"outcome":"Safety (topical)","grade":"C","grade_meaning":"weak human evidence","effect_size":"not measurable","adverse":true,"human_studies":"2 RCTs","evidence":"Topical 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.","references":[{"citation":"Mahlapuu M, et al. Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial.","where":"Wound Repair Regen, 2021","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC9298190/"}]}],"regions":[{"region":"European Union","status":"Unauthorised medicinal product","note":"No marketing authorisation. Supplying it for human use is an offence under national medicines law."},{"region":"United States","status":"Not approved; compounding withdrawn","note":"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."},{"region":"United Kingdom","status":"Unlicensed medicine","note":"Selling or supplying it for human use is an offence."},{"region":"Australia","status":"Schedule 4, unapproved","note":"Prescription-only substance not on the ARTG."},{"region":"Canada","status":"Not authorised","note":"No DIN; selling it is illegal."},{"region":"Sport (WADA)","status":"Prohibited at all times","note":"Unapproved anywhere, so it falls under S0 (non-approved substances)."}],"faq":[{"q":"Does LL-37 heal wounds?","a":"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."},{"q":"Is LL-37 an antibiotic?","a":"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."},{"q":"Is injected LL-37 anti-inflammatory?","a":"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."}],"references":[{"cite":"Grönberg A, et al. Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial.","where":"Wound Repair Regen, 2014; DOI 10.1111/wrr.12211","url":"https://pubmed.ncbi.nlm.nih.gov/25041740/","note":"34 patients, phase 1/2a."},{"cite":"Mahlapuu M, et al. Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial.","where":"Wound Repair Regen, 2021","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC9298190/","note":"148 patients, phase 2b; primary endpoint not met."},{"cite":"Reviews of LL-37 biology in infection, wound repair and autoimmunity.","where":"Various","url":"https://pubmed.ncbi.nlm.nih.gov/?term=LL-37+cathelicidin+review+psoriasis+inflammation","note":"Preclinical mechanism; no systemic human data."}],"last_reviewed":"2026-09-03","literature_searched_to":"2026-09-03","changelog":[{"date":"2026-09-03","note":"Initial publication from the two topical wound-healing trials."}],"license":"CC BY 4.0 — cite as “LYO Research” with a link.","methodology":"https://lyoresearch.com/methodology"}