LL-37: the body’s own antimicrobial peptide, and why injecting it is not obviously a good idea
Genuine innate immunity, well characterised, made by your own cells and dependent on vitamin D. It also has a documented role in driving autoimmune inflammation, which is the part that rarely accompanies the enthusiasm.
Regulatory status. Research compound — no FDA approval for systemic peptide therapy use. That is the app’s own field, reproduced here rather than summarised. It means no regulator has reviewed a manufacturer’s evidence for identity, purity, potency or safety in people for this compound, so nothing below is a marketing claim about a product you can buy.
Purity, identity and concentration are therefore unverified by anyone but whoever made the vial. The storage rule in the fact box below is general practice for this formulation rather than a specification for a particular product: General handling practice for this formulation. Your supplier’s own insert or COA overrides anything here.
This page names no vendor, no clinic and no testing service, and there is no discount code anywhere on this site — the moment a page like this recommends where to buy, it stops being information.
- Also known as
- Cathelicidin, CAMP peptide
- Class
- Peptide
- Regulatory status
- Research compound — no FDA approval for systemic peptide therapy use.
- Before mixing
- Sealed powder tolerates room temperature in transit, but keep it refrigerated at 2–8 °C (36–46 °F) for anything beyond a few weeks, or frozen for months. Keep it dark — the carton it shipped in is doing a job.
- After mixing
- Once reconstituted with bacteriostatic water: refrigerate at 2–8 °C and use within about 28 days. The benzyl alcohol in bacteriostatic water is what buys that window — plain sterile water has no preservative, so a vial mixed with it should be treated as one sitting only. Kits are usually ten vials: only the one you mixed is on that 28-day clock — the sealed ones keep their own, much longer shelf life, so store them as powder, not as solution.
- What ruins it
- Do not freeze a reconstituted vial. Repeated freeze–thaw is one of the more reliable ways to degrade a peptide.
- Handling caveat
- General handling practice for this formulation. Your supplier’s own insert or COA overrides anything here.
What it is and what it does
Established clinical use LL-37 is the active fragment of hCAP18, the only cathelicidin humans make. It is produced by neutrophils, macrophages and epithelial surfaces, and it disrupts bacterial membranes directly, neutralises endotoxin, and acts as a signalling molecule — recruiting immune cells, promoting wound repair, and interfering with biofilms. That is textbook innate immunity rather than a claim.
Established clinical use Its production is directly vitamin D dependent: the gene carries a vitamin D response element, and cathelicidin expression falls when vitamin D is low. That is a real and well-established link, and it is the single most actionable thing on this page — a person with low vitamin D and an interest in LL-37 has a cheaper, safer and better-evidenced route to raising it. The vitamin D page covers how the number is read and why the optimal band is contested.
The double edge
Established clinical use LL-37 is not simply protective. In psoriasis it complexes with self-DNA and self-RNA and drives plasmacytoid dendritic cells to produce interferon, which is a core mechanism of the disease; it is a recognised autoantigen in psoriasis and has been implicated in lupus, rheumatoid arthritis and atherosclerosis. Elevated cathelicidin is a feature of several inflammatory conditions rather than a marker of good defence.
That is why the app’s drawbacks list says it may exacerbate autoimmune conditions, and it is a stronger caution than that phrasing suggests. Administering more of a peptide that is part of the pathogenic mechanism in psoriasis, to someone with psoriasis, is not a neutral act. Anyone with an autoimmune or autoinflammatory diagnosis should treat this as a conversation with the clinician managing it rather than a supplement decision.
Animal-only or theoretical Local injection-site inflammation is the common practical effect and follows from the same biology — it is an inflammatory mediator, so injecting it inflames things.
Evidence and sourcing
Animal-only or theoretical There is no published randomised trial of systemic LL-37 for any indication. Topical work in wound healing exists and is more advanced; the systemic use is extrapolation. The app records no half-life, because none has been published, which is why the fact box carries no pharmacokinetic rows.
There is also a delivery problem intrinsic to the molecule: peptides of this kind are degraded quickly and bind serum proteins, so how much of an injected dose reaches anywhere useful in an active form is unknown.
No approved product, so identity and purity rest with whoever made the vial. The app’s panel — complete blood count, vitamin D, CRP — is sensible, and vitamin D is on it for the reason above rather than as a formality. This site names no vendor.
The dosing rows the app records
Off-label or community practice Reproduced from the app’s reference so you can see what it holds, not as a recommendation. Which row applies to a particular person, if any, is a clinical decision this page does not make — and rows describing supraphysiological or post-cycle use are filtered out before this table is built, so what you see here is a subset.
| Label | Amount | Route and frequency | Duration recorded |
|---|---|---|---|
| Immune and Antimicrobial | 100-200mcg | SubQ 2-3x weekly | 4-6 weeks |
| Wound healing topical | Apply to wound | 1-2x daily | Until healed |
What the app monitors alongside it
The panel below is the app’s own monitoring note for LL-37, verbatim. The analytes in it that have a page here are linked; those pages cover what each one measures, which assay produced it and how to read a trend.
- Monitoring panel
- CBC (immune cells), Vitamin D levels (essential), CRP. Monitor injection sites for local reactions.
Drawbacks and risks the app records
From the app’s own entry, and the autoimmune item deserves more weight than its position gives it — this peptide is part of the disease mechanism in psoriasis.
- Can cause injection site inflammation locally
- May exacerbate autoimmune conditions
- Limited human trial data for systemic use
- Topical vs systemic effects differ significantly
- Sourcing and purity critical
- Not FDA approved
Questions people actually ask
Is vitamin D a better route to raising it?
For most people, yes. Cathelicidin expression is directly vitamin D dependent, and correcting a low vitamin D is cheaper, safer and far better evidenced than injecting the peptide.
Why would an antimicrobial peptide be a problem in autoimmunity?
Because in psoriasis it complexes with self-nucleic acids and drives interferon production — it is a recognised autoantigen there, and it has been implicated in lupus and rheumatoid arthritis. More of it is not obviously better.
Is there trial evidence for injecting it?
None published for systemic use. Topical wound-healing work is further along, and the systemic use is extrapolation from it and from the basic immunology.
Why does the injection site react?
Because it is an inflammatory signalling molecule as well as an antimicrobial one. Local inflammation is the mechanism working, not an impurity.
Where the load-bearing numbers come from
Named rather than linked. Publisher URLs move, and a citation that resolves to a 404 two years from now is worse than one you can search for by name — every entry below is findable from the title and year alone.
- Cathelicidin structure and innate immune function
- Standard immunology; LL-37 is the only human cathelicidin
- Vitamin D dependence
- The cathelicidin gene carries a vitamin D response element; expression falls with deficiency
- Role in psoriasis and autoimmunity
- Established in the psoriasis literature as a self-nucleic-acid complexing autoantigen driving interferon production
- Absence of systemic trial and pharmacokinetic data
- No published randomised trial of systemic administration; app.html holds no half-life entry
A peptide whose effect depends on what is already inflamed is one to log alongside the symptoms. TherapyLog keeps both.
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