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Limited human dataNot FDA approved

LL-37

Also known as: LL37 · LL 37 · Cathelicidin · Human cathelicidin antimicrobial peptide · CAP-18 · hCAP-18 fragment · Ropocamptide

Updated 34 sources

LL-37 is the only cathelicidin humans make: a 37 amino acid antimicrobial peptide released by white cells, skin and gut lining. People inject 100 to 250 mcg a day for infection, gut and immune goals, but no injection has been tested in people. The human trials are topical, on leg and foot ulcers, with mixed results.
Calculate with LL-37Dosage chart

Quick facts

Half-life
  • Not measured in humans after injection. One guide cites about 15 to 30 minutes in serum, unsourced.
  • About 30 minutes for the free peptide, cleared by protease breakdown, per one guide; it adds that human data are lacking.
  • About 4 to 6 hours, per one guide, with no source.
Routes
  • Subcutaneous injection
  • Topical
  • Other route
Forms
  • Vial (powder)
  • Topical
Reported dose ranges
  • 25 to 750 mcg (subcutaneous injection)
  • 0.01 to 3.2 mg/mL (topical)
  • 250 mcg (other route)
Vial sizes
  • 5 mg, 10 mg
Chemistry
  • 4,493 g/mol · C205H340N60O53 · CAS 154947-66-7
FDA status
  • Not FDA approved
WADA
  • Not confirmed

What people use LL-37 for

  • Chronic or recurrent infections and biofilms
  • Gut barrier problems, dysbiosis and SIBO
  • General immune support, often framed around low vitamin D
  • Lyme and mould-illness protocols
  • Chronic wounds, applied topically

How it is thought to work. LL-37 folds into a positively charged helix that inserts into microbial membranes and breaks them open. It also binds bacterial endotoxin, calls in neutrophils and monocytes through the FPRL1 receptor, and supports new blood vessels and skin regrowth. The same signalling can amplify inflammation, which is why it is tied to psoriasis and rosacea. Vitamin D switches on its gene.

LL-37 dosing

18 protocols from studies, guides and community reports, grouped by goal. Tap a source badge to see where a number came from.

Venous leg ulcer gel2

Venous leg ulcer gel (trial)

Amount
0.5 to 3.2 mg/mL
How often
Twice weekly, applied to the ulcer
Route
Topical, topical
Cycle
4 weeks of treatment
Timing and details

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Venous leg ulcer gel (Phase IIb)

Amount
0.5 to 1.6 mg/mL
How often
Twice weekly at dressing changes, with compression
Route
Topical, topical
Cycle
13 weeks
Timing and details

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Other protocols: injected14

Community daily structure

Amount
100 to 500 mcg
How often
Once daily, often 5 days on and 2 off
Route
SubQ, vial (powder)
Cycle
2 to 4 weeks, then a break of 2 weeks or more
Rest
2 weeks or more
Timing and details

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Weekly ladder

Amount
50 to 400 mcg
How often
Once daily, optionally 5 days on and 2 off
Route
SubQ, vial (powder)
Cycle
8 to 12 weeks, up to 16
Titration (8 steps) and details

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Immune support

Amount
100 to 200 mcg
How often
Once daily
Route
SubQ, vial (powder)
Cycle
4 to 8 weeks; one guide cycles 8 weeks on, 4 off
Rest
4 weeks off
Titration (2 steps) and details

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Gut barrier

Amount
100 to 200 mcg
How often
Once daily
Route
SubQ, vial (powder)
Cycle
4 to 8 weeks
Timing and details

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Conservative start

Amount
25 to 50 mcg
How often
Daily
Route
SubQ, vial (powder)
Cycle
1 to 2 weeks, then reassess

Standard (every day or every other day)

Amount
100 mcg
How often
Daily or every other day
Route
SubQ, vial (powder)
Cycle
4 to 8 weeks
Timing and details

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Higher daily

Amount
200 mcg
How often
Daily
Route
SubQ, vial (powder)
Cycle
4 to 6 weeks at most

Tolerance test dose

Amount
100 mcg
How often
Once, then wait 48 to 72 hours
Route
SubQ, vial (powder)
Timing and details

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Chronic infection, 3 times a week

Amount
200 to 500 mcg
How often
3 times a week (Mon, Wed, Fri), dropping to twice weekly in the taper
Route
SubQ, vial (powder)
Cycle
8 weeks
Rest
4 weeks off
Titration (3 steps) and details

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Short daily course

Amount
250 to 500 mcg
How often
Daily
Route
SubQ, vial (powder)
Cycle
2 to 4 weeks
Timing and details

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Extended induction then maintenance

Amount
500 mcg
How often
Daily for 4 to 6 weeks, then 3 times a week for 8 to 16 weeks
Route
SubQ, vial (powder)
Cycle
12 to 22 weeks in total
Rest
4 to 8 weeks
Timing and details

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Pulse course

Amount
500 to 750 mcg
How often
Daily
Route
SubQ, vial (powder)
Cycle
2 to 4 weeks, then a long break
Timing and details

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Acute infection (community)

Amount
200 to 400 mcg
How often
Once daily
Route
SubQ, vial (powder)
Cycle
2 to 4 weeks
Timing and details

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Anecdotal low daily

Amount
125 mcg
How often
Daily
Route
SubQ, vial (powder)

Other protocols: topical, topical1

Topical solution on a wound

Amount
0.01 to 0.05 mg/mL
How often
Once or twice daily until the wound closes
Route
Topical, topical
Timing and details

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Other protocols: other route1

Intratumoral injection (trial)

Amount
250 mcg
How often
Once weekly into each injected tumour
Route
Other route
Cycle
Up to 8 weeks
Timing and details

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Doses shown are what sources report, labelled by origin. Not medical advice.

Full LL-37 dosage guideEvery titration step in syringe units, missed doses and how to mix.

Vial strengths and syringe units

Every LL-37 vial size with the water volumes sources use. Units are what to draw on a U-100 insulin syringe, worked out exactly.
LL-37: concentration and U-100 syringe units for each vial size and water volume
WaterStrength100 mcgdose, units200 mcgdose, units500 mcgdose, units
5 mg vial
1 mLCompetitor guide5 mg/mL20.02 mL40.04 mL100.1 mL
2 mLCompetitor guide2.5 mg/mL40.04 mL80.08 mL200.2 mL
3 mLCompetitor guide1.667 mg/mL60.06 mL120.12 mL300.3 mL
10 mg vial
2 mLCompetitor guide5 mg/mL20.02 mL40.04 mL100.1 mL
Units are on a U-100 insulin syringe (100 units = 1 mL). U-50 and U-30 barrels read the same units.Water volumes from

Doses shown are what sources report, labelled by origin. Not medical advice.

Calculate with this peptideYour vial, your water, your dose: LL-37 in syringe units, with the math shown.

LL-37 side effects

What trials and labels report, kept apart from what users and guides report. Frequencies are worded as each source states them.

Reported in studies and labels2

From clinical trials and regulatory documents.

  • Widespread skin eruption after intratumoral dosing

    One published case from the melanoma trial; resolved within 2 months of stopping

  • Topical use in ulcer trials

    No local or systemic safety concerns at 0.5 to 3.2 mg/mL; well tolerated at 0.5 and 1.6 mg/mL in 148 patients

Reported by users and guides6

From community reports and dosing guides. Not measured rates.

  • Injection-site redness, swelling, itching or burning

    The most common report with subQ use; lasts 12 to 48 hours

    How people manage it

    • Inject slowly over 3 to 5 seconds

  • Flushing or warmth near the site

    Linked to LL-37 releasing histamine from mast cells

  • Flu-like symptoms with the first doses

    Some users; usually fades with continued dosing, more often at higher doses

    How people manage it

    • Start lower and titrate up

  • Low-grade fever, fatigue and body aches in the first days

    Commonly reported in forum aggregates, read by users as immune activation

  • Headache or mild fatigue

    Less common

  • Herx-like flare

    Less common; blamed on bacterial die-off as biofilms break up

    How people manage it

    • Start at 100 mcg and increase gradually
All 9 LL-37 side effects and how people manage themEvery management tip, who should not use it, and side-effect questions.

Who should avoid it

  • Psoriasis, lupus or rosaceaCondition

    LL-37 is tied to disease activity in all three: it turns self-DNA into an immune trigger and is raised in rosacea skin.

  • Mast cell activation syndromeCondition

    One guide lists it as a strong relative contraindication; LL-37 releases histamine from mast cells.

  • Active or past cancerCondition

    FDA cites nonclinical tumour promotion in some tissues; lab data show growth of lung cancer and melanoma cells.

  • Pregnancy or breastfeedingCondition

    No safety data.

Storage

Powder (before mixing)

Temperature
-20 °C

Freezer at -20 C, dry and dark. Sellers state 24 or 36 months at -20 C. One guide says room temperature or fridge is fine for powder.

Mixed vial

Temperature
2 to 8 °C
Use within
7 to 30 days

Fridge at 2 to 8 C, dark, never frozen. Use-by advice runs from 7 to 30 days; 28 to 30 days is the most common figure. LL-37 breaks down in solution, so mix small batches.

Mixed vial

Temperature
2 to 8 °C
Use within
14 to 21 days

Most forum users report finishing a mixed vial within 2 to 3 weeks.

Mixed with: Bacteriostatic water

Mixing. Doses are small, so a 30 or 50 unit syringe reads more easily. The solution should be clear and colourless; discard it if cloudy.

Stacks people report

Combinations from guides and community posts, with the reason given.
  • BPC-157

    The usual gut and wound pairing: LL-37 100 to 200 mcg a day subQ with BPC-157 250 to 500 mcg a day, for 4 to 8 weeks. LL-37 for microbes, BPC-157 for repair.

  • Thymosin Alpha-1

    Immune pairing: LL-37 100 to 200 mcg a day with thymosin alpha-1 1.6 mg 2 to 3 times a week, for 4 to 8 weeks.

  • KPV

    Gut pairing: LL-37 100 to 200 mcg a day subQ with oral KPV 200 to 500 mcg a day, adding an anti-inflammatory to the antimicrobial.

  • TB-500

    Infected-wound pairing: LL-37 with TB-500 2 to 2.5 mg twice weekly, for 4 to 6 weeks.

  • Retatrutide

    PeptIQ app users most often co-log LL-37 with retatrutide (3 of 6 reports). Co-use, not a designed stack.

Compare LL-37

Evidence and legal status

Evidence: limited human data

Human data are topical or intratumoral only. A 34-person venous ulcer trial favoured the lowest strength; the 148-person Phase IIb missed overall, with a possible benefit in large ulcers. A diabetic foot ulcer cream trial improved granulation. A 4-person melanoma injection study exists. No subQ, oral or systemic trial found.

FDA and WADA

Not FDA approved

An approval withdrawn, or removed from FDA's compounding lists.

Not FDA approved. FDA lists cathelicidin LL-37 among substances previously in 503A Category 2 whose nominations were withdrawn, and flags immunogenicity, impurity and nonclinical safety concerns. A law-firm summary reports FDA plans to take it to its compounding advisory committee before February 2027. Its developer, Promore Pharma, named it ropocamptide for its topical wound trials.

Not named on the WADA 2026 Prohibited List. The S0 class covers any pharmacological substance without human therapeutic approval, which on its plain wording could include LL-37. No source addresses this directly. A law-firm summary says FDA slated LL-37 for a separate advisory committee review expected before February 2027; removal from Category 2 does not by itself allow compounding.

WADA: Not confirmed

LL-37 questions

What is LL-37?

The only cathelicidin your body makes: a 37 amino acid peptide cut from a larger protein, hCAP-18. Neutrophils, skin and gut lining release it. It punches holes in bacterial membranes and also calls in immune cells.

What is LL-37 used for?

In peptide circles: chronic infection and biofilm support, gut barrier problems, general immune support and wounds. The only human trials are topical, on leg and foot ulcers. Claims for Lyme, gut or systemic infection have no human data.

What dose do people use?

Community write-ups cluster at 100 to 250 mcg subQ once daily, often 5 days on and 2 off, for 2 to 4 weeks. Guides start at 25 to 100 mcg and some go to 500 or 750 mcg. No injection dose has been tested in people.

How many units is 250 mcg?

With 5 mg in 2 mL of water, 250 mcg is 10 units on a U-100 syringe. With 5 mg in 1 mL it is 5 units. Use the calculator for other mixes.

How long should a cycle be?

Short blocks of 2 to 4 weeks with 2 or more weeks off are the most common. Some guides run 8 to 12 weeks, rarely 16. No cycle length has been validated.

Why does the injection burn or itch?

LL-37 releases histamine from mast cells, so warmth, redness and itch at the site are the most common complaint. Inject slowly, start low and rotate sites.

Does injected LL-37 heal wounds like the studies?

Nobody knows. Every wound trial put a gel or cream on the ulcer. In the first trial (34 people) the lowest strength, 0.5 mg/mL, healed best. The larger 148-person trial found no overall benefit, only a possible one in large ulcers.

Can people with psoriasis, lupus or rosacea use it?

Guides say be very careful or skip it. LL-37 bound to self-DNA drives interferon signalling in psoriasis, and rosacea skin carries abnormally high cathelicidin.

Does LL-37 raise cancer risk?

There is no human data. FDA notes nonclinical findings that it can promote tumours in some tissues. In lab and mouse work it grew lung cancer cells and may help melanoma invade. Guides say avoid it with active or past cancer.

What does vitamin D have to do with it?

Active vitamin D switches on the cathelicidin gene, so low vitamin D means less LL-37. One guide says to fix vitamin D before trying the peptide.

What is the half-life?

Not measured in people after injection. Guides quote anything from 15 to 30 minutes to 4 to 6 hours with no source. Serum also blunts its antibacterial action in lab tests.

How long does mixed LL-37 last?

Keep it at 2 to 8 C. Advice runs from 7 days to 30 days, and forum users usually finish a vial in 2 to 3 weeks. It breaks down in solution, so mix only what you will use.

Is LL-37 FDA approved?

No. FDA lists cathelicidin LL-37 among substances that were in Category 2 until the nomination was withdrawn, and flags immunogenicity, impurity and nonclinical safety concerns. It was not part of the July 2026 committee vote. The developer calls it ropocamptide.

Is it banned in sport?

It is not named on the WADA 2026 list. S0 bans any substance with no human therapeutic approval, which on its plain wording could cover it. Tested athletes should treat it as off limits.

Ask about LL-37

Answers come from this site's pages only, with a link to each source.

Sources

34 sources, each checked by date. Record updated Oct 24, 2026. Numbers are restated in our own words and labelled by where they came from.

Regulatory4

  1. Certain bulk drug substances for use in compounding that may present significant safety risksFDA · checked Oct 24, 2026
  2. FDA signals potentially evolving stance toward compounding of certain peptidesGoodwin Procter, via a news report · checked Oct 24, 2026
  3. FDA panel votes to loosen restrictions for four peptidesPharmExec, via a news report · checked Oct 24, 2026

Reference work2

  1. CathelicidinWikipedia · checked Oct 24, 2026
  2. LL-37, CID 16198951PubChem · checked Oct 24, 2026

Vendor guide4

  1. LL-37 5 mg product pageVendor product page · checked Oct 24, 2026
  2. LL-37 5 mg product pageVendor product page · checked Oct 24, 2026
  3. LL-37 5 mg product pageVendor product page · checked Oct 24, 2026

Competitor guide7

  1. LL-37 dosage guidebodyhackguide.co · checked Oct 24, 2026
  2. LL-37 peptide protocol guidepeptidedosingprotocols.com · checked Oct 24, 2026
  3. LL-37 protocol guidepathtopeptides.com · checked Oct 24, 2026

Community-reported3

  1. LL-37 community protocols and reportspeptideprotocolwiki.com, via a competitor guide · checked Oct 24, 2026
  2. LL-37 dosage calculator and chart (anecdotal dose)peptides.org, via a competitor guide · checked Oct 24, 2026
  3. LL-37 wiki, app user log datapeptiq.io, via a competitor guide · checked Oct 24, 2026