LL-37 Guide

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.

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.

The full step-by-step protocol examples, titration, and printable protocol sheet are planned for a future paid Protocol Playbook module.

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.

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.

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.

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.

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