What Is LL-37? Dosage, Half-Life & How to Track It
Also known as: Cathelicidin LL-37 · hCAP-18 (precursor) · CAP-18
LL-37 is the only cathelicidin peptide the human body makes — a 37-amino-acid fragment cut from a precursor protein (hCAP-18) that fights bacteria directly and modulates the immune response around a wound or infection. Community protocols run it subcutaneously once daily, commonly 100–400 mcg, titrated up over roughly eight weeks. Like most small peptides its human half-life isn’t well documented, so the schedule is built on caution rather than a measured number. Educational only.
What LL-37 is and how it works
LL-37 takes its name from its structure — 37 amino acids, starting with two leucines — cleaved from a precursor protein called hCAP-18 (human cationic antimicrobial protein 18), also known by the older name CAP-18. It’s the only cathelicidin the human body produces, stored in neutrophils and released at sites of injury or infection.
Mechanistically, it’s a broad-spectrum antimicrobial: it’s positively charged (cationic) and inserts directly into the negatively charged membranes of bacteria, disrupting them — a mechanism bacteria have a much harder time evolving resistance to than they do against conventional antibiotics. Beyond killing microbes outright, it recruits and activates immune cells, promotes wound-related blood-vessel growth, and — in a finding that got significant attention — has been shown in mouse studies to help reactivate dormant hair-follicle stem cells after wounding, part of why it shows up in hair-regrowth research.
Most of that depth is preclinical or in-vitro; human trial data specific to the injectable protocols in community use is thin, and it isn’t FDA-approved for any of these uses.
Typical dosing & reconstitution
LL-37 comes lyophilized and is reconstituted with bacteriostatic water. Community protocols run it subcutaneously once daily, often starting around 50 mcg and titrating up over roughly eight weeks toward 300–400 mcg; some run a 5-days-on, 2-days-off week instead of straight daily.
Reconstitution sets the concentration, and the concentration sets your units:
| Vial | BAC water | Concentration | 1 unit (U-100) ≈ |
|---|---|---|---|
| 5 mg | 3 mL | 1.67 mg/mL | 16.7 mcg |
At 1.67 mg/mL, a 200 mcg dose is 12 units. Run your own vial and water through the reconstitution calculator to lock in the exact units for your dose.
Half-life & what it means for frequency
There’s no formally published human half-life for LL-37. It’s cleared and broken down like other small cationic peptides — fast, on the order of minutes to a couple of hours is the reasonable assumption, not a documented figure. That’s the basis for once- (or twice-) daily dosing.
The 5-on/2-off variant some protocols use suggests the effect people are chasing doesn’t require every single day, but there’s no hard pharmacokinetic data settling that either way — it’s a scheduling preference, not a strict requirement.
What to track & common side effects
Generally reported as well tolerated at community doses; injection-site irritation is the most common complaint. Because it’s immune-modulating, anyone with an active autoimmune condition should loop in a doctor before starting — an activated immune peptide isn’t a place to guess.
What’s worth tracking: dose and site each day, whichever specific outcome motivated starting it (skin, wound healing, hair), and whether you’re on a titration ladder or a maintenance dose — details that are easy to lose without a log.
How to track LL-37 in Frontload
Log LL-37’s daily (or 5-on/2-off) dose and site so the schedule is tracked for you instead of guessed at. Note the outcome you’re watching — skin, wound, hair — next to each entry so you can tell whether eight weeks in, the trend actually moved.
Model it yourself · free, no account
Reconstitution Calculator
Model it yourself: enter your vial size and BAC water and the Peptides tab returns concentration and the exact units for any dose — the same math built into the Frontload app.
Related compounds
Related reading: What peptides can you mix in the same syringe? · Peptide reconstitution math: how much BAC water to add
Frequently asked questions
What is LL-37 used for?
LL-37 is studied as the body’s own broad-spectrum antimicrobial and immune-modulating peptide — direct antibacterial action, wound-related blood-vessel growth, and (in animal studies) reactivating hair-follicle stem cells after wounding. Human clinical data is limited and it isn’t FDA-approved for any of these uses.
What is the half-life of LL-37?
Not formally published in humans. As a small cationic peptide it’s assumed to clear quickly, consistent with once- or twice-daily community dosing, but there’s no measured figure to cite.
How do you reconstitute LL-37?
Add bacteriostatic water to the lyophilized vial — a common setup is 3 mL into a 5 mg vial, giving about 1.67 mg/mL, so one insulin-syringe unit is roughly 16.7 mcg. The reconstitution calculator handles any vial-and-water combination.
Is LL-37 the same thing as cathelicidin?
Yes — LL-37 is the active peptide cleaved from hCAP-18, the only cathelicidin precursor protein humans make. “Cathelicidin” is the protein family name; LL-37 is the specific 37-amino-acid piece studied and sold as a peptide.
This is educational information, not medical advice. Doses and protocols above reflect published references and community practice — protocol decisions belong with your prescribing physician. Generic names used throughout. How this reference is built & how the AI is tested →
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