Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.
LL-37 at a glance
- What it is
- A 37-residue amphipathic host-defense peptide cleaved from the human cathelicidin precursor hCAP-18
- Researched for
- Antimicrobial, antibiofilm, wound-healing and immunomodulatory activity (preclinical and early clinical research)
- Commonly reported range
- ~100–500 mcg per administration in community reports (no established human protocol)
- Route reported
- Subcutaneous injection most commonly reported; topical and oral used in some studies
- Reported frequency
- Once daily to several times weekly in community reports
- Reported cycle
- ~2–4 weeks in reports; topical study protocols ran up to 4 weeks
- Plasma half-life
- Short; estimated on the order of ~1 hour, highly dependent on proteolysis
- Regulatory status
- Not FDA-approved; investigational/research-use-only; verify WADA status independently
Reported ranges from research/community — examples, not recommendations.
What it is / mechanism
LL-37 is the only member of the cathelicidin family expressed in humans, released when the precursor protein hCAP-18 is proteolytically cleaved by serine proteases such as proteinase 3. The mature 37-amino-acid peptide carries a net positive charge of about +6 and folds into an amphipathic alpha-helix, most strongly in the presence of negatively charged microbial membranes. This cationic, amphipathic structure lets it bind bacterial membranes and, depending on lipid composition, either form transient pores or disrupt the membrane, killing Gram-positive and Gram-negative bacteria, some fungi, and enveloped viruses. Beyond direct killing, research describes immunomodulatory roles: LL-37 signals through receptors such as formyl peptide receptor 2 (FPR2/FPRL1), influences chemotaxis, binds nucleic acids, and modulates inflammatory cytokine responses and tissue-repair pathways. These are described mechanisms from laboratory research, not clinically guaranteed effects in humans.
Researched effects
Reported and studied activities include broad-spectrum antimicrobial and antibiofilm action, antiviral and antifungal effects in vitro, modulation of inflammation, promotion of angiogenesis and wound closure in preclinical models, and community reports of use for gut and skin support. These are research findings and community reports, not guaranteed outcomes; much of the evidence is preclinical (cell and animal) and human clinical data remain limited. LL-37 also has context-dependent biology: elevated endogenous LL-37 has been associated in the literature with chronic inflammatory and autoimmune conditions, which is why researchers emphasize its narrow window between beneficial and cytotoxic concentrations.
Evidence & regulatory status
- Evidence: Extensive in vitro and animal research documents membrane-disrupting antimicrobial activity and immunomodulatory signaling; human clinical evidence is early and limited, with one topical study and small trials reported.
- Regulatory: LL-37 is not approved by the FDA for any therapeutic use and is considered investigational; it is sold and handled as a research-use-only material, not a medicine.
- Research-use: All dosage figures here are examples reported in the literature or community, provided for educational context only and are not a protocol or recommendation for human use.
Dosage — reported ranges (overview)
There is no established or approved human dosing protocol for LL-37, and it has a notably narrow margin between antimicrobial and cytotoxic concentrations, so precision matters in any research context. As examples of what is reported, not a recommendation: community subcutaneous reports commonly fall around 100–500 mcg per administration, once daily or several times weekly, over roughly 2–4 week periods; some sources describe conservative starting points near 100–125 mcg daily. Published human work has largely used topical (roughly 0.5–1.6 mg/mL applied twice weekly) or oral routes, while injectable dosing appears mainly in preclinical animal models (e.g., mg/kg ranges in rodents). These figures are illustrative examples only and are not medical advice or a suggested human dose.
A printable protocol sheet with a reconstitution reference and an injection log comes with All-Access Lifetime.
Reconstitution — bac-water math
Reconstitution is simply concentration math: you add bacteriostatic water to the lyophilized powder and calculate how much peptide sits in each measured volume. On a U-100 insulin syringe, 100 units equals 1 mL. For an mcg-dosed peptide, concentration in mcg/mL = (vial mg × 1000) ÷ mL of water added, and the units to draw = dose in mcg ÷ concentration × 100. Worked example: a representative 5 mg vial reconstituted with 2 mL of bacteriostatic water gives (5 × 1000) ÷ 2 = 2500 mcg/mL. A 250 mcg example dose would then be 250 ÷ 2500 × 100 = 10 units on a U-100 syringe. Add the water slowly against the vial wall and swirl gently; do not shake, as agitation can damage the peptide.
| Bac water added | Concentration | 250 mcg | 500 mcg |
|---|
| 1 mL | 5000 mcg/mL | 5 units (0.05 mL) | 10 units (0.10 mL) |
| 2 mL | 2500 mcg/mL | 10 units (0.10 mL) | 20 units (0.20 mL) |
| 3 mL | ~1667 mcg/mL | 15 units (0.15 mL) | 30 units (0.30 mL) |
This is concentration math, not a dose recommendation.
Injection / administration basics
In studies and community reports, LL-37 is most often described as a subcutaneous injection using a small-gauge insulin syringe, with the drawn volume determined by the concentration math above. General aseptic handling reported in the literature includes swabbing the vial stopper and injection site, drawing slowly, and rotating sites; LL-37 solution is unstable and reported to degrade in water, so reconstituted material is kept refrigerated and used promptly. This describes handling reported in research contexts and is not medical instruction or a personal dose.
Half-life & frequency rationale
LL-37 has a short functional half-life, estimated on the order of roughly one hour in cellular contexts, though this is highly dependent on proteolytic degradation; when protease activity is inhibited, reported half-lives extend substantially (over 12 hours in some experiments). In solution the peptide is chemically unstable, which is why researchers reconstitute it fresh and store it cold.
Side effects, safety & contraindications
Human safety data are limited. Reported topical use has been described as well tolerated with a low rate of side effects, and small oral studies reported no serious adverse events. Key research concerns include LL-37's narrow window between antimicrobial and cytotoxic concentrations, potential local irritation at injection sites, and the fact that elevated endogenous LL-37 has been linked in the literature to chronic inflammatory and autoimmune conditions (such as certain skin and lung diseases). Because controlled human injectable safety data are scarce, its risk profile in that route is not well characterized.
Stacking — overview
In community and product contexts LL-37 is most often combined with other repair- and immune-oriented peptides, particularly for gut, skin, and inflammation research themes. The most frequently discussed pairing is with BPC-157 and KPV as a combined gut and immune support concept, and it is sometimes grouped with tissue-repair peptides like TB-500 and GHK-Cu. These are examples of commonly reported pairings, not recommendations, and combining peptides increases uncertainty around safety and interactions.
Gut & Immune Trio
LL-37 + BPC-157 + KPV
Repair & Recovery Stack
LL-37 + BPC-157 + TB-500
Skin & Tissue Support
LL-37 + GHK-Cu
Stacking across compounds
The overview above covers LL-37. The cross-compound material — which pairings are redundant rather than additive, where interaction risk is documented versus merely unstudied, and the blend arithmetic worked end to end — lives in the Peptide Stacking Guide, which is free to read in outline and $39 in full (included with All-Access Lifetime).
Included with this guide
The LL-37 Stacking Module
The overview above is the free summary. The LL-37 Stacking Module goes through each combination in depth — the mechanism-level reason it is proposed, what is actually reported in practice, and the cautions specific to that pairing — plus what to avoid and why. Included with LL-37 Standard Access.
- How to think about stacking LL-37 — 4 principles
- 3 combinations covered in detail
- What to avoid, and why — 3 items
- Combination-specific cautions
Combinations covered: Gut & Immune Trio, Repair & Recovery Stack, Skin & Tissue Support.
For how combinations are grouped by research context, the named blends, and why a pre-mixed blend vial cannot be calculated from its total milligrams, see the peptide stacks guide.
Storage & handling
- Lyophilized (freeze-dried) powder is reported to be stable when kept sealed, cold, and protected from light; refrigeration is common and long-term freezing is used for extended storage.
- Once reconstituted, LL-37 is unstable in solution and should be refrigerated (about 2–8°C / 36–46°F), protected from light, not frozen or shaken, and used promptly since it degrades over time.
References
Compiled from peer-reviewed literature on cathelicidin/LL-37 biology (mechanism, membrane activity, immunomodulation, half-life) and community and vendor dosing references; all figures are educational examples, not medical advice.
Related peptide guides
Continue exploring related educational guide topics in the Medibact library.
Guide FAQ
Quick answers about guide scope, access, and educational use context.
Is LL-37 approved by the FDA?
No. LL-37 is not FDA-approved for any therapeutic use. It is considered investigational and is handled as a research-use-only material, not a medicine.
What dose of LL-37 is reported in research?
There is no established human protocol. Community subcutaneous reports commonly cite around 100–500 mcg per administration, but these are examples only, not a recommendation, and published human work has mostly used topical or oral routes.
How do I reconstitute a 5 mg LL-37 vial?
Add bacteriostatic water slowly and swirl gently without shaking. For example, 2 mL of water in a 5 mg vial yields 2500 mcg/mL, so a 250 mcg example dose equals 10 units on a U-100 insulin syringe.
What is LL-37's half-life?
It is short, estimated on the order of about one hour in cellular contexts, and highly dependent on proteolysis. In solution the peptide is unstable, so it is stored cold and used promptly.
Is LL-37 banned by WADA?
LL-37 is not specifically named on the WADA Prohibited List the way some peptides are, but WADA categories are broad and change over time. Athletes should independently verify current WADA status before any use, and note it is not an approved medicine.
Compliance and trust notes
- Educational content only; no personalized health or outcome claims.
- No personalized use recommendation outputs.
- Use this material for general learning and research-context literacy.
