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Research peptide

What is LL-37?

LL-37 explained in plain English: what it is, what the research shows, side effects, legal status and dosage, plus a calculator for syringe units. Doses shown come only from the label or published trials, each with its source. Also called Cathelicidin, CAP-18 fragment, hCAP-18.

LL-37 is not approved for human use by the FDA or any other regulator. This page is educational; talk with a qualified healthcare professional before using any substance.

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= 5,000 mcg

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Syringe, no result yetU-100, 1 mL syringe holding up to 100 units. Enter your dose.0102030405060708090100

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What is LL-37?

LL-37 is the only human cathelicidin, a 37-amino-acid peptide the body makes to fight infections. Its name comes from its length and its first two amino acids, two leucines (L).

Skin, gut, lung and immune cells release it when they detect an infection or injury. A lab-made version is sold online as a research peptide.

What does LL-37 do?

LL-37 kills bacteria, viruses and fungi by breaking open their outer membranes, and it calls in other immune cells. It also helps wounds heal by encouraging new skin and blood vessels to form.

Vitamin D switches on the gene that makes it, which is one way vitamin D supports the immune system.

What does the research on LL-37 show?

The human research is about wound creams, not injections. A 2014 trial found LL-37 applied to hard-to-heal venous leg ulcers sped up healing, but a larger 2021 trial found no overall benefit, only in patients with large wounds.

A small 2023 trial of LL-37 cream in diabetic foot ulcers reported faster healing. There are no human trials of injected LL-37 for immunity, infections or anything else.

LL-37 side effects and risks

The risks of injecting LL-37 are unknown. LL-37 can drive inflammation as well as fight infection, and high levels are linked to skin diseases like psoriasis and rosacea.

Products sold online aren’t checked for purity, strength or sterility.

LL-37 is not approved for human use by the FDA or any other regulator. Its nomination was withdrawn from the FDA’s list of compounding substances with safety concerns, which is not an approval.

How do you reconstitute LL-37?

LL-37 research vials hold a freeze-dried powder that is mixed with bacteriostatic water. The calculator above turns the vial size, the water and a dose into syringe units, and the reconstitution guide explains each step.

See the dosage section below for what is known about doses, with sources.

LL-37 dosage in clinical trials

LL-37 has only been tested in people as a treatment applied to wounds, not as an injection. In the first venous leg ulcer trial it was applied at two strengths.

Doses tested in published clinical trials. They are not approved doses, and trial participants were closely monitored.

LL-37 doses, with sources
WhenDoseHow often
Venous leg ulcer trial (applied to the wound)0.5 mg/mL or 1.6 mg/mL solution[1]Applied to the ulcer during the trial
  1. Grönberg et al. (2014), Wound Repair and Regeneration

Medical disclaimer: this dosage information is for education only and comes from the source shown for each row. It is not medical advice and not a recommendation for you. Only a licensed prescriber who knows your health can decide whether LL-37 is right for you and at what dose. Don't start, change or stop a medicine based on this page, and don't use research peptides or unapproved drugs based on trial doses.

LL-37 concentration chart

The concentration of a LL-37 vial depends only on its size and the water you add. Each unit on a U-100 syringe holds one hundredth of a mL.

LL-37 concentration by vial size and water
Vial + waterConcentrationPer unit (U-100)
5 mg + 1 mL5,000 mcg/mL (5 mg/mL)50 mcg per unit (0.05 mg per unit)
5 mg + 2 mL2,500 mcg/mL (2.5 mg/mL)25 mcg per unit (0.025 mg per unit)
5 mg + 3 mL1,666.67 mcg/mL (1.66667 mg/mL)16.67 mcg per unit (0.01667 mg per unit)

Frequently asked questions

What does LL-37 do?

It is part of the immune system. LL-37 kills bacteria, viruses and fungi directly and signals other immune cells, and it also takes part in wound healing.

Is LL-37 safe to inject?

That is unknown. Injected LL-37 has not been tested in human trials, and too much LL-37 is linked to inflammation in skin diseases like psoriasis and rosacea.

Does vitamin D raise LL-37?

Yes. Vitamin D switches on the gene that makes LL-37 in skin and immune cells, which is one reason vitamin D matters for immunity.

Sources

  1. Grönberg et al. (2014), LL-37 for hard-to-heal venous leg ulcers, Wound Repair and Regeneration
  2. Mahlapuu et al. (2021), Multicentric trial of LL-37 in venous leg ulcers
  3. FDA, Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks

Last updated .

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