Immune & antimicrobial

LL-37

Also called cathelicidin LL-37, human cathelicidin, hCAP18 (precursor protein), CAMP (gene)

LL-37 is the only cathelicidin-type germ-fighting peptide made by the human body. It is found in skin, airways and white blood cells, where it helps kill microbes and steer inflammation and wound healing. A small human trial tested it as a topical treatment for leg ulcers, but it is not an approved drug anywhere.

Early human dataSome small human studies exist; evidence is limited.

All printable flashcards

Drawn from its published sequence: 37 residues, one bead each.

Overview

How it works

Established in lab studies: LL-37 is a positively charged, helix-forming peptide that binds to and disrupts the membranes of bacteria, fungi and some viruses. It also has immune-signaling roles (proposed and partly established), including attracting immune cells, influencing cytokine release, and promoting new blood vessel growth and skin-cell migration in wounds. It can also be pro-inflammatory: high levels are linked to skin diseases such as rosacea and psoriasis.

What research shows

Venous leg ulcers (Grönberg et al. 2014, randomized placebo-controlled phase 1/2 trial, n=34): topical LL-37 gel twice weekly for 4 weeks at three strengths; the two lower strengths (0.5 and 1.6 mg/mL) were associated with better ulcer healing than placebo, while the highest (3.2 mg/mL) was not; treatment was well tolerated.
Extensive lab and animal research shows broad antimicrobial activity and effects on wound healing and inflammation.
Human observational research links abnormal LL-37 levels to skin conditions such as rosacea and psoriasis.

Doses studied in people

Study or label	Dose used	Source
Phase 1/2 randomized placebo-controlled trial in hard-to-heal venous leg ulcers (n=34)	Topical gel at 0.5, 1.6 or 3.2 mg/mL, applied twice weekly for 4 weeks	¹

The only published human dosing is topical, on wounds; there are no published human trials of injected LL-37.

Read this first: these are the amounts given to participants in published studies or written on official prescribing labels, reported for reference. They are not recommendations. Trial doses were chosen for specific patients under medical supervision, and a dose that is safe in one person can be harmful in another.

Weekly protocol

How the schedule looks week by week. Each chart says where it comes from: a prescribing label, a clinical trial, or a protocol commonly reported online.

Venous leg ulcer trial (Grönberg 2014)

Clinical trial

One week

D1D2D3D4D5D6D7

Twice weekly · Topical gel on the wound

Dose by week

0.5, 1.6 or 3.2 mg/mL gel (by study group)wk 1–4

Course: 4 weeks
Note: Randomized placebo-controlled trial in hard-to-heal venous leg ulcers. There are no human trials of injected LL-37.
Source: Grönberg A et al. Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial. Wound Repair Regen 2014

Commonly reported injection protocol

Commonly reported, not studied

One week

D1D2D3D4D5D6D7

Once daily · Subcutaneous injection

Syringe units (U-100)

Vial Water added

Dose by week

50 mcgwk 1

100 mcgwk 2

150 mcgwk 3

200 mcgwk 4

250 mcgwk 5

300 mcgwk 6

350 mcgwk 7

400 mcgwk 8

Supplies for one course (estimate)

Counts only. This site does not sell or link to supplies.

Course: 8–12 weeks (up to 16)
Note: Some protocols use 5 days on, 2 off. Another guide lists 100–200 mcg daily, 5 days a week, for 2–4 weeks, then 2 weeks off.
Source: PeptideDosages.com: LL-37 (5 mg vial) dosage protocol
Also: Peptide Protocol Wiki: LL-37 dosing protocols

Reference only, not a recommendation. Charts marked "commonly reported" describe what public sources say people use. They have not been tested in trials, and their safety and effect are unknown. Label and trial schedules were set for specific patients under medical supervision. Use the calculator only to understand the arithmetic.

Vial math

Many research vials hold 5 or 10 mg of powder. This table shows how much ends up in each mark on a U-100 insulin syringe for common amounts of added liquid. It is arithmetic only, not a dose.

Vial	Liquid added	Concentration	Per unit (0.01 mL)
5 mg	1 mL	5 mg/mL	50 mcg	Open in calculator
5 mg	2 mL	2.5 mg/mL	25 mcg	Open in calculator
5 mg	3 mL	1.67 mg/mL	16.7 mcg	Open in calculator
10 mg	1 mL	10 mg/mL	100 mcg	Open in calculator
10 mg	2 mL	5 mg/mL	50 mcg	Open in calculator
10 mg	3 mL	3.33 mg/mL	33.3 mcg	Open in calculator

More sizes: all vial sizes · How this works: Syringes and units · Reconstitution guide.

Safety

Topical use in the leg-ulcer trial was well tolerated, with no safety concerns reported (Grönberg 2014).
FDA cited immunogenicity and impurity risks and a lack of human safety data when it placed LL-37 in Category 2 (2023).
Because LL-37 can drive inflammation in some skin diseases, effects outside a wound setting are not well understood (lab and observational data).
Unknown long-term safety; no data on injected use.

Report side effects of any drug or product to the FDA through MedWatch. For a possible poisoning in the US, call Poison Control at 1-800-222-1222.

Legal status

FDA: Not FDA-approved; investigational
Compounding: 503A: placed in Category 2 in Sept 2023; removed April 15, 2026 (effective about April 22) after nomination withdrawal. Removal does not make it legal to compound; it is not on the 503A bulks list. FDA plans a PCAC review before the end of February 2027.
Sports (WADA): Not named on the 2026 Prohibited List; as a substance with no current government approval for human therapeutic use, it would likely fall under S0 (non-approved substances), prohibited at all times. Athletes should confirm with their anti-doping organization.
Other: Sold online as a 'research chemical'; FDA has warned online peptide sellers that 'research use only' labels do not exempt products intended for people.

Rules change often. See Legal status of peptides for how these categories work.

History

Human cathelicidin was identified in the mid-1990s by Swedish researchers (Agerberth, Gudmundsson and colleagues). Lipopeptide Pharmaceuticals (Sweden) developed it as a topical wound treatment (LL-37/'LL-37 for venous leg ulcers') and published a phase 1/2 trial in 2014. In the US it was placed in FDA's 503A Category 2 in September 2023 and removed on April 15, 2026 (effective about April 22) after its nomination was withdrawn; FDA plans an advisory committee review before the end of February 2027.

Common questions

Is LL-37 an approved drug?

No. It is investigational, and in 2023 FDA placed it in Category 2, its list of substances that may pose significant safety risks in compounding ⁵.

What does the human research show?

In a small randomized trial of 34 people with hard-to-heal leg ulcers, the two lower strengths of LL-37 gel were linked to better healing than placebo, but the highest strength was not ¹.

What doses were tested in people?

The only published human trial used a gel on leg ulcers at 0.5, 1.6 or 3.2 mg/mL, applied twice weekly for 4 weeks ¹. No human trials of injected LL-37 have been published ¹².

Is LL-37 safe?

The topical gel was well tolerated in the leg-ulcer trial ¹. LL-37 can also drive inflammation and is linked to skin conditions like rosacea and psoriasis, so effects outside wounds are not well understood ².

Can LL-37 be compounded?

FDA removed it from Category 2 in April 2026 after its nomination was withdrawn, but that does not make it legal to compound ³⁴⁵. An FDA advisory committee review is planned before the end of February 2027 ⁴.

Is LL-37 banned in sport?

It is not named on WADA's 2026 list, but as an unapproved substance it would likely fall under S0, prohibited at all times ⁶.

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Sources

Last reviewed 2026-10-25 · How we research · Found an error? See our corrections policy.