Broad-spectrum antimicrobial activity including biofilms [2]
Demonstrated in vitro against Gram-positive and Gram-negative bacteria, fungi and some viruses, with activity against biofilms and multi-drug-resistant organisms.
PrecisePep/Peptide Library/LL-37
Immune & Anti-Inflammatory
LL-37
cathelicidin antimicrobial peptide · CAP-18 fragment · hCAP18(104-140)
The only antimicrobial peptide the human body makes in the cathelicidin family — a direct bacterial killer that is also a powerful immune signal, and whose biology cuts in both directions depending on context.
00 Overview
LL-37 is not an invented compound — it is a component of human innate immunity. It is the only member of the cathelicidin family in humans, released by cleavage of the precursor protein hCAP18 and expressed by neutrophils, epithelial cells and keratinocytes. Its transcription is directly regulated by vitamin D receptor signalling, which is the mechanistic backbone of the long-observed relationship between vitamin D status and infection resistance.[1]
It does two very different jobs. It kills microbes directly by permeabilising bacterial membranes — including against biofilms and antibiotic-resistant organisms, which is why it attracts genuine pharmaceutical interest. And it is a signalling molecule: chemotactic for immune cells, modulating cytokine responses, neutralising endotoxin, and promoting wound healing and angiogenesis.[2]
The complication is that the second job has a dark side. LL-37 is implicated in the pathogenesis of psoriasis, rosacea, lupus and atherosclerosis. In psoriasis it complexes with self-DNA to break tolerance and drive plasmacytoid dendritic cell activation — it is a recognised autoantigen in the disease.[3] This is not a theoretical concern invented for a caveat; it is a substantial literature about a molecule people inject.
An endogenous molecule with a genuine autoimmune literature
Most "risk" sections on this site describe unknowns. This one describes a known: elevated LL-37 is causally implicated in psoriasis and is a target of autoantibodies in lupus. Administering more of it is not a neutral act in anyone with, or predisposed to, those conditions — and nobody buying it is being screened.
// Mechanism of action
Direct antimicrobial action. LL-37 is cationic and amphipathic: it binds negatively charged bacterial membranes and disrupts them. Because the mechanism is physical rather than enzymatic, resistance develops less readily than to conventional antibiotics, and it retains activity against biofilms and against Gram-positive and Gram-negative organisms alike.
Endotoxin neutralisation. It binds lipopolysaccharide, blunting the inflammatory cascade triggered by Gram-negative bacterial debris — relevant to sepsis research and to gut-derived endotoxin.
Immune signalling. Chemotactic for neutrophils, monocytes and T cells via FPRL1; modulates dendritic cell maturation and cytokine output. This is the part with two directions: context determines whether the net effect is resolution or amplification.
Wound healing and angiogenesis. Promotes keratinocyte migration and re-epithelialisation and stimulates angiogenesis, contributing to the wound-repair interest.
Vitamin D dependence. The CAMP gene encoding hCAP18 contains a vitamin D response element. Adequate vitamin D status is a prerequisite for endogenous production — which raises an obvious question about whether correcting a deficiency is the more sensible intervention.
01 Reported benefits
Effects that have been reported. A study-tier entry means a result was published — not that the effect is established, reproducible, or transferable from a rodent to a person.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Endotoxin (LPS) neutralisation [2]
Binds and neutralises lipopolysaccharide, attenuating downstream inflammatory signalling.
Wound healing and re-epithelialisation [2]
Promotes keratinocyte migration and angiogenesis; impaired LL-37 expression is associated with poor healing in chronic wounds.
Vitamin D–cathelicidin axis in infection resistance [1]
Vitamin D receptor signalling directly induces cathelicidin expression — a well-characterised link and a plausible mechanism behind vitamin D status and infection outcomes.
Clinical evaluation in chronic wounds [4]
LL-37 has been evaluated in human trials for hard-to-heal venous leg ulcers, with dose-dependent findings reported — among the few genuine human interventional datasets for any compound in this category.
Implicated in psoriasis and autoimmune pathogenesis [3]
LL-37 complexed with self-DNA activates plasmacytoid dendritic cells and breaks tolerance; it is a recognised autoantigen in psoriasis and features in lupus and rosacea literature. This sits in the study tier because it is well-evidenced — it is simply not a benefit.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Chronic and biofilm-associated infection
The most mechanistically supported use case, and the one driving pharmaceutical interest. Community use for chronic sinus, gut and Lyme-adjacent complaints is an extrapolation from in vitro activity to complex clinical syndromes.
Gut dysbiosis and SIBO
Proposed on antimicrobial and endotoxin-neutralising grounds. A non-selective antimicrobial acting on a microbiome is not obviously a targeted intervention.
Acne and inflammatory skin conditions
Cuts directly against the rosacea and psoriasis literature, where LL-37 is part of the problem. Direction of effect is genuinely uncertain here.
Antiviral and immune support
In vitro antiviral activity is documented; clinical translation is not.
Correcting vitamin D deficiency may be the better route
If the objective is adequate cathelicidin activity, restoring the upstream regulator is cheap, measurable, evidence-based and does not involve injecting an autoantigen.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Improvement in chronic gut and sinus complaints
The dominant community report, typically over two to four weeks, often in the context of longstanding unresolved symptoms.
Strong injection-site reactions
Reported more consistently than for most peptides — redness, swelling and pain. Consistent with a molecule whose job is to recruit immune cells.
Flu-like symptoms after dosing
Reported particularly at higher doses, and interpreted by users as a die-off or immune-activation response.
Skin flares
Reported by a minority — which is exactly what the psoriasis and rosacea literature would predict.
Nebulised use for respiratory complaints
Reported in community practice. Delivering an immune-activating peptide into the lungs has no supporting data and a plausible inflammatory downside.
02 Adverse effects & risks
Adverse effects, contraindications and unknowns. The grey-market tier is where under-reporting is worst: uncontrolled use produces no systematic safety surveillance at all, so absence of a reported harm is not evidence of safety.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Pro-inflammatory in the wrong context [3]
The same immune-signalling activity that resolves infection amplifies inflammation in psoriasis, rosacea, lupus and atherosclerosis. This is the best-evidenced risk on the page.
Cytotoxicity at higher concentrations [2]
LL-37 permeabilises mammalian as well as bacterial membranes above a threshold concentration — the selectivity is relative, not absolute.
Local reactions in clinical wound studies [4]
Human trial work reported local tolerability issues at higher doses.
No systemic human safety dataset
The clinical work is topical or local. Repeated systemic subcutaneous administration in healthy adults has not been characterised.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Triggering or worsening autoimmune disease
Follows directly from the psoriasis and lupus literature. Anyone with a personal or family history of psoriasis, rosacea or connective-tissue disease is in the group this concerns most.
Microbiome disruption
A broad-spectrum antimicrobial does not distinguish between problematic and commensal organisms.
Atherosclerosis progression [3]
LL-37 is present in atherosclerotic plaque and implicated in plaque inflammation. Uncharacterised for exogenous administration.
Angiogenic activity
The same concern that attaches to the repair peptides — promoting vessel growth is not selectively beneficial.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Marked injection-site inflammation
The most consistent complaint by a wide margin.
Flu-like malaise, chills, fatigue
Common in the first days, usually settling.
Skin flares and worsened rosacea
A minority report that aligns exactly with the published disease biology.
Headache
Occasionally reported.
03 Dosing ranges
Figures below are documented, not recommended. Study ranges come from published protocols in the stated model; grey-market ranges are what the research community reports using and carry no safety validation of any kind.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Topical dosing in wound trials [4]
Human clinical work used topical application to chronic wounds at defined concentrations, with local tolerability limiting the upper range.
No established systemic human dose
Every subcutaneous figure in circulation is community-derived.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Short courses, not continuous use
An immune-activating antimicrobial is a poor candidate for indefinite administration, and the autoimmune literature reinforces that.
Check vitamin D status first
If cathelicidin activity is the goal, the upstream regulator is measurable and correctable. This is the single most sensible thing on this page.
Dilute well and rotate sites
Practical mitigation for the reliably reported injection-site inflammation.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
100 mcg daily, escalating slowly
The common entry approach — starting low specifically because of the injection-site and flu-like reactions.
250–500 mcg daily
The typical community range for a short course.
2–4 week courses
Short courses are the norm, unlike most repair peptides.
Nebulised for respiratory use
Reported; unsupported and mechanistically questionable given the inflammatory potential in lung tissue.
| Approach | Dose | Route | Duration |
|---|---|---|---|
| Entry / titration | 100 mcg | Subcutaneous | 3–5 days |
| Standard | 250 – 500 mcg | Subcutaneous, daily | 2–4 weeks |
| Topical (evidenced route) | Per preparation | Topical to wound | Per protocol |
04 Synergy & interactions
Combination effects. Almost no peptide combination has been studied as a combination in humans; stack logic is overwhelmingly mechanistic inference and community practice. Each linked compound has its own page.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
No combination studies exist
No study combines LL-37 with another research peptide.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
LL-37 + vitamin D [1]
The one mechanistically grounded pairing: vitamin D drives endogenous cathelicidin expression. It is also an argument for the vitamin rather than the peptide.
LL-37 + BPC-157 / KPV for gut work
Antimicrobial action alongside barrier repair and NF-κB suppression. The KPV pairing is interesting in principle because it pairs an immune activator with an immune suppressor — which may be complementary or may be self-cancelling.
Caution with immunosuppressive therapy
Adding an immune activator to established immunosuppression, or to biologic therapy for an autoimmune condition, is uncharacterised and directionally worrying.
Caution: existing inflammatory skin disease
The clearest contraindication logic available for any compound on this site.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Stacked with gut-repair peptides
The commonest context, typically alongside BPC-157 or KPV.
05 Protocols
Whole schedules — dosing, titration, cycle length, and off-time — as documented in trials, as proposed from mechanism, and as circulated in the research community. Reproduced for study and comparison only.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Chronic wound clinical protocol [4]
Topical application at defined concentrations with healing endpoints and local tolerability monitoring.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Screen for autoimmune and inflammatory skin history first
The one contraindication with a genuine published basis rather than an inferred one.
Measure vitamin D before reaching for the peptide
Cheap, standard, and addresses the upstream regulator.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
2–4 week course, titrated from a low dose
The general community pattern.
Not part of either documented protocol
Neither the Gold Standard Protocol nor the 15-Compound Matrix includes it.
05b Condition-specific interest
There is one finding on this page that changes how the whole compound should be read, and it is not a benefit. Intradermal injection of LL-37 is a standard method for inducing rosacea-like disease in mice. Not a side effect observed in passing — it is how the animal model is made. Anyone injecting this compound should know that before they read anything else here.
No approval, no trial
LL-37 is not approved anywhere and has no human efficacy trial for any indication. It is the sole human cathelicidin, and it is a genuine and important part of innate immunity — which is a different claim from it being a sensible thing to administer. Its concentration in tissue is tightly regulated, and several inflammatory and autoimmune skin diseases are characterised by having too much of it in the wrong place.
Actionable warning — the most important item here
Rosacea — LL-37 injection is the animal model
Pathophysiology
Rosacea involves a hyperactive TLR2–kallikrein 5–cathelicidin pathway. Kallikrein 5 cleaves cathelicidin into pro-inflammatory fragments, and those fragments drive the vascular and inflammatory features of the disease. Lesional rosacea skin has elevated LL-37.
Mechanistic rationale
Researchers induce rosacea-like skin disease in mice by injecting LL-37 intradermally. The model is well established, the mechanism is characterised through mast cell degranulation and NLRP3 inflammasome activation, and blocking those pathways attenuates the lesions. That is not an obscure finding — it is the standard preclinical rosacea model. A compound that reliably produces a disease when injected is a poor candidate for injection, and this is not something the market for it mentions.
Community reports
Facial flushing, erythema and irritation are reported by users and are generally attributed to a histamine response or to "detox". They are also exactly what the animal model produces.
Components carrying the argument: Cathelicidin fragments, mast cells, NLRP3
Actionable warning — well characterised
Psoriasis — LL-37 is a T-cell autoantigen
Pathophysiology
Psoriasis is a T-cell-mediated autoimmune skin disease with a central role for type I interferon and the IL-23/IL-17 axis.
Mechanistic rationale
LL-37 is overexpressed in psoriatic lesions, and it does two distinct things there. It complexes with self-DNA released from dying cells and converts it into a potent stimulus for plasmacytoid dendritic cells through TLR7 and TLR9, driving type I interferon and breaking innate tolerance to self-DNA. And it functions as a T-cell autoantigen in its own right, presented by HLA-C*06:02 and activating autoreactive T cells directly. Administering more of a molecule that is an autoantigen in a common autoimmune disease deserves more thought than it usually receives.
Community reports
Not discussed in community spaces. Anyone with psoriasis, or a family history of it, has a specific reason to avoid this compound rather than a general one.
Components carrying the argument: Self-DNA complexes, type I interferon, direct autoantigen
Theorized — same mechanism, broader implication
Lupus and interferon-driven autoimmunity
Pathophysiology
Systemic lupus erythematosus is characterised by loss of tolerance to nucleic acids and a type I interferon signature.
Mechanistic rationale
The mechanism above — cathelicidin complexing with self-DNA to trigger interferon production — is implicated in lupus as well as psoriasis, and neutrophil extracellular traps carrying LL-37 are one proposed route into that process. The implication generalises: this molecule is part of how tolerance to self-DNA breaks down, not merely a bystander in diseases where it happens to be elevated.
Community reports
Not raised in community use.
Components carrying the argument: LL-37–DNA complexes, pDC activation
Theorized — the claimed use, in vitro
Antimicrobial and antibiofilm activity
Pathophysiology
Antimicrobial resistance and biofilm-associated infection are genuine and serious problems that resist conventional antibiotics.
Mechanistic rationale
LL-37 has broad-spectrum antimicrobial and anti-biofilm activity in vitro, and host-defence peptides are a serious research field for exactly this reason. The field also has a long record of failing at the toxicity and stability stages, and the properties that make LL-37 effective locally — membrane disruption and pro-inflammatory signalling — are the same ones that make systemic administration a problem. Self-directed use of an antimicrobial also contributes to the resistance problem it is marketed as solving.
Community reports
Used for chronic and difficult-to-treat infections, frequently in Lyme and biofilm-focused communities. No human data supports any of it.
Components carrying the argument: Membrane disruption, broad-spectrum activity
Theorized — genuine role, narrow window
Wound healing and skin barrier
Pathophysiology
Cathelicidin is upregulated in wounded skin and contributes to re-epithelialisation and angiogenesis.
Mechanistic rationale
The role in normal wound repair is real and well described. The difficulty is that it is a concentration-dependent and location-dependent role: the same molecule that supports repair at physiological levels drives inflammatory disease when it is elevated, which is what the rosacea and psoriasis entries above describe. This is not a compound with a wide therapeutic window.
Community reports
Used topically and by injection for wound and skin applications, often in blends.
Components carrying the argument: Re-epithelialisation, angiogenesis
Actionable — and it is the useful part of this page
The upstream alternative nobody mentions
Pathophysiology
Cathelicidin expression is directly regulated by vitamin D. The vitamin D receptor binds a response element in the cathelicidin gene promoter, which is one of the better-characterised mechanisms linking vitamin D status to innate immune function.
Mechanistic rationale
If the goal is adequate cathelicidin, the physiological route is to correct vitamin D deficiency and let the body produce it where and when it is needed, at regulated concentrations. That is cheap, measurable by a standard blood test, has an established safety profile, and avoids delivering a fixed dose of an autoantigen systemically. Vitamin D deficiency is common and under-corrected.
Community reports
Vitamin D status is rarely checked by people buying LL-37, which is the more striking omission given how directly the two are connected.
Components carrying the argument: Vitamin D receptor → cathelicidin gene expression
| Condition | LL-37 role | Implication |
|---|---|---|
| Rosacea | Elevated — injection induces the animal model | A reason not to inject it |
| Psoriasis | T-cell autoantigen; drives interferon | Specific reason to avoid if affected |
| Lupus | Self-DNA complexes → interferon | Part of how tolerance breaks |
| Infection / biofilm | Active in vitro | The claimed use; no human data |
| Wound healing | Genuine physiological role | Narrow window — concentration matters |
| Vitamin D | Directly regulates its expression | The upstream route, measurable and cheap |
What actually has evidence for these conditions
For infection: culture-directed antibiotic therapy, source control, and vaccination. Antimicrobial stewardship exists because self-directed antimicrobial use drives the resistance that makes infections untreatable.
For rosacea: trigger avoidance, topical ivermectin, metronidazole or azelaic acid, oral doxycycline at anti-inflammatory dose, brimonidine for erythema, and vascular laser for telangiectasia. Note that doxycycline works here partly by inhibiting the kallikrein pathway that cleaves cathelicidin — the treatment reduces the activity of this molecule.
For psoriasis: topical corticosteroids and vitamin D analogues, phototherapy, methotrexate and ciclosporin, and the biologic classes targeting TNF, IL-17 and IL-23 — which have transformed outcomes and work by suppressing the axis LL-37 helps drive.
For innate immune support: check and correct vitamin D. It is the regulator of the gene that produces this peptide, it is a cheap blood test, and it is the intervention with an actual evidence base.
06 Handling, reconstitution & storage
Physical-chemistry reference for laboratory handling of the lyophilised material. Reproduced so that stability and concentration mathematics can be studied — see the calculator for the arithmetic and the reconstitution guide for sterile technique.
Reconstitution
Supplied lyophilised, commonly 5 mg per vial. Reconstituted with bacteriostatic water; generous dilution is widely reported to reduce injection-site reactions.
Storage
Lyophilised: −20 °C. Reconstituted: 2–8 °C.
Common vial sizes
Commonly 5 mg lyophilised vials.
Stability notes
A 37-residue cationic peptide; avoid agitation. Cationic peptides can adsorb to glass and plastic surfaces, which is a real consideration at low concentrations.
07 Legal & regulatory status
Regulatory status changes and differs by country. This is a summary for orientation, not legal advice — check your own jurisdiction.
Not approved for human use. LL-37 has been the subject of clinical investigation for chronic wounds but holds no marketing approval in any jurisdiction. Supplied as a research chemical.
Regulatory update — current as at August 2026
LL-37 (cathelicidin) is scheduled for review by the FDA's Pharmacy Compounding Advisory Committee before the end of February 2027, alongside Melanotan II, LL-37 (cathelicidin), Dihexa acetate and PEG-MGF — whichever of those is not this compound.
This follows the FDA's April 2026 restructuring of the Section 503A categories and the July 2026 meeting at which six peptides (BPC-157, KPV, TB-500, MOTS-c, Semax and Epitalon) were recommended for the Bulks List and one (emideltide/DSIP) was not. Nothing has been decided for LL-37 (cathelicidin).
A PCAC recommendation is not an approval, and the 503A Bulks List is not a drug approval either. It is also worth knowing that July 2026 was the second round: across two sittings in October and December 2024 the same committee reviewed seven substances — among them ipamorelin, kisspeptin-10, AOD-9604, CJC-1295 and thymosin alpha-1 — and rejected all seven. Two separate things are being conflated in almost every write-up of the 2026 decision:
- The vote is advisory. PCAC recommendations are non-binding. The pathway from here runs: removal from Category 2 (done, April 2026) → PCAC recommendation (done, July 2026) → placement in Category 1 through notice-and-comment rulemaking, which commonly takes eight to twelve months → and the HHS Secretary must sign off on any addition to the list. Nothing is lawfully compoundable on the strength of the vote alone.
- Even a successful listing would not make these approved drugs. Inclusion on the 503A Bulks List permits a licensed compounding pharmacy to use the substance in a compounded preparation for an individual patient with a prescription. It says nothing about the compound being demonstrated safe and effective — no efficacy trial is required, and none of these has one.
- It would not legitimise research-chemical supply. A compounding pathway runs through a licensed pharmacy and a prescriber. Grey-market vials labelled "research use only" are not that, and nothing in this decision changes their status.
Regulatory and trial claims re-checked against primary sources on 16 August 2026. Checked: psoriasis autoantigen and rosacea induction-model literature. Approvals, trial readouts and compounding decisions move faster than anything else on this page — a date here means someone looked, not that nothing has changed since.
Anti-doping
Athletes subject to WADA, USADA, UKAD, NCAA or military testing should assume any peptide is prohibited unless they have verified otherwise against the current WADA Prohibited List. Several classes here (growth-hormone secretagogues, TB-4 analogues, metabolic modulators) are explicitly named. Check the current list — it is republished annually.
§ Sources & further reading
Links resolve to PubMed records, trial registries, publisher pages or primary documents. Where a body of work rather than a single paper is cited, the link opens a PubMed query so the full result set — including newer papers than this page — can be reviewed. Verify every claim against the primary source before relying on it.
- PubMed: vitamin D receptor signalling and cathelicidin (CAMP) induction (live query)Database or literature search
- PubMed: LL-37 — antimicrobial activity, biofilms, endotoxin neutralisation and wound healing (live query)Database or literature search
- PubMed: LL-37 in psoriasis, lupus, rosacea and atherosclerosis — autoantigen and pro-inflammatory role (live query)Database or literature search
- PubMed: LL-37 clinical trials in hard-to-heal venous leg ulcers (live query)Database or literature search
Reminder
For educational and research reference only. Nothing on this site is medical advice, a recommendation, or an instruction to administer any substance to a human being. Every figure on this page is a record of what has been reported, not a recommendation. Full disclaimer.