Immune & defense Host-defense antimicrobial peptide
LL-37
Regulatory status
Status at a glance
503A compounding status
Not nominated
We found no pending nomination for the 503A bulks list. Unless the substance has another legal pathway (for example, a USP monograph or use in an FDA-approved drug), 503A pharmacies generally may not compound with it.
- FDA approval
- Not FDA-approved for any use
- 503B outsourcing
- Not determined
- Anti-doping (WADA)
- Not on the WADA Prohibited List
- DEA schedule
- Not a controlled substance
About peptide status
Most peptides discussed here are not FDA-approved for any use, and products labeled “research use only” are not for human use. Removal from Category 2 does not authorize compounding. PCAC votes are non-binding recommendations; FDA and HHS make the final decisions.
This is not medical or legal advice, and we do not publish dosing, sourcing or reconstitution information. Talk with a licensed clinician before using any peptide.
If you think you are having a medical emergency, call 911.
Key takeaway
LL-37 is the body's natural antimicrobial "host-defense" peptide, intensely studied as part of the immune system and sold on the "research peptide" market for antimicrobial and immune support. Its biology is well described, but there is no approved product and no human efficacy evidence for the injected wellness use, and its effects are context-dependent. As of 2026 it is not FDA-approved.
At a glance
- FDA status
- Non-FDA-approved peptide sold in the wellness/gray market
- What it is
- The only human cathelicidin, a natural antimicrobial and immune-signaling peptide
- Research
- Biology well studied, but no human efficacy evidence for the injected wellness use
- Effects
- Context-dependent; can be pro- or anti-inflammatory
- Evidence strength
- Low research
Summary
LL-37 is the body's antimicrobial host-defense peptide. See how it works, what research shows, and why it is not FDA-approved as of 2026.
What is LL-37?
LL-37 is the active 37-amino acid fragment of the only human cathelicidin, a natural host-defense (antimicrobial) peptide produced by immune and skin cells. It is a well-studied part of the body's innate immune system. It is sold through wellness and "research peptide" channels for antimicrobial and immune support, and it is not an approved medicine.
How does it work?
LL-37 has two broad actions. Its positively charged, membrane-active structure can directly disrupt the membranes of microbes, and it also modulates the immune system, influencing immune-cell recruitment, inflammation, and wound healing, and binding some microbial factors. These roles are documented in a large laboratory and animal literature. Importantly, its effects are context-dependent: it can be either pro- or anti-inflammatory and has been implicated in some inflammatory skin diseases. This describes its biology, separate from demonstrated benefit from giving it as a therapy.
Is it FDA-approved?
Safety note
Status: Non-FDA-approved peptide sold in the wellness/gray market
Category: Wellness and performance · Primary body area: Immune & defense
No. There is no FDA-approved exogenous LL-37 therapeutic, and gray-market versions are unapproved. It was not among the peptides reviewed favorably at the 2026 FDA compounding advisory meetings.
What does the research show?
Editor’s note
Evidence strength: Low research
There is a rich endogenous and preclinical science base, but no approved product and no human efficacy data for the injected wellness use, and its biological effects are context-dependent.
The evidence is preclinical for any injected wellness use. LL-37's biology in innate immunity, wound healing, and skin disease is documented in humans and in extensive laboratory work, including studies of how it disrupts microbes and binds microbial factors (example).
However, there are no controlled human trials establishing efficacy or safety of self-administered LL-37 for antimicrobial, immune, or healing wellness uses, and its context-dependent, sometimes pro-inflammatory, behavior argues against simple benefit claims.
Sources: laboratory work on LL-37's antimicrobial and immune actions (Zsila and Beke-Somfai, Biochemical and Biophysical Research Communications, 2020, DOI: 10.1016/j.bbrc.2020.03.162), indexed on PubMed. This document is educational, is not medical advice or a health claim, and is not an offer to sell any product.
Registered human trials
0 registered human trials on ClinicalTrials.gov that we reviewed
Sources
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- [15]
- [16]
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