Summary
LL-37 is the 37 amino acid antimicrobial (germ-killing) peptide that human neutrophils (a type of white blood cell) and skin cells release from the hCAP18 protein. The only human trials are of a gel applied to hard to heal venous leg ulcers (sores caused by poor vein circulation): a 34 patient phase I/II trial (an early stage study) found faster healing at two of three doses, and a larger phase IIb trial did not meet its primary endpoint, its main goal, in the full population. It is not FDA approved for any use; FDA removed it from the 503A Category 2 list (compounding ingredients flagged for significant safety risks) on April 15, 2026, and it has not been added to the 503A bulks list (ingredients pharmacies may use to compound drugs for individual patients).
What is LL-37?
LL-37 is a human cathelicidin antimicrobial peptide (37 amino acids, cleaved from the hCAP18 precursor). It is also known as Cathelicidin LL-37, hCAP18 C-terminal peptide, Human cathelicidin antimicrobial peptide, Ropocamptide, CAP-18.
How does it work?
LL-37 is amphipathic and cationic. It disrupts bacterial membranes, neutralizes lipopolysaccharide, and acts as a chemoattractant for neutrophils, monocytes, and T cells through the formyl peptide receptor FPR2. In wound models it stimulates keratinocyte migration, angiogenesis, and re-epithelialization, and it modulates toll-like receptor signaling. High concentrations are cytotoxic to human cells, which is why the topical wound trials tested a narrow dose range.
| Cluster | Immune and antimicrobial |
|---|---|
| Routes | Topical gel on chronic wounds (clinical trials); Subcutaneous injection (as sold, no human data); Nebulized or intranasal (as sold, no human data) |
| Conditions studied | Wound healing; Immune support and immune deficiency; Autoimmune disease |
| Record | v2, draft, verified Sep 22, 2026 |
What does the evidence say about LL-37?
Two randomized placebo controlled trials of topical LL-37 in venous leg ulcers exist. The phase I/II trial (n = 34) found the 0.5 mg/mL and 1.6 mg/mL gels healed ulcers faster than placebo, while 3.2 mg/mL did not. The larger phase IIb trial did not meet its primary endpoint across all patients and reported a signal only in a subgroup with larger ulcers. There are no human trials of injected or systemic LL-37, which is the form sold online.
| Evidence type | Indexed studies | Participants (human) |
|---|---|---|
| Human randomized trials | 2 | 34 |
| Human observational studies | 0 | n/a |
| Animal studies | 1 | n/a |
| All indexed studies | 3 | 34 |
Human evidence
Gronberg 2014: 34 adults with hard to heal venous leg ulcers randomized to placebo or LL-37 gel at 0.5, 1.6, or 3.2 mg/mL twice weekly for 4 weeks. The two lower doses produced significantly faster healing rates than placebo with no dose limiting toxicity; the highest dose was not better than placebo. Mahlapuu 2021: a multicenter phase IIb trial of the two lower doses in venous leg ulcers that did not reach its primary endpoint in the whole study population. No human data exist for subcutaneous injection, nebulized, or oral LL-37.
Animal evidence
In mice and rats, LL-37 applied to wounds or delivered by gene transfer accelerated re-epithelialization and angiogenesis, and LL-37 or its analogs protected against bacterial infection in skin, lung, and sepsis models. Rodent work also shows pro inflammatory and cytotoxic effects at higher concentrations, and LL-37 is elevated in psoriasis and rosacea lesions, where it is thought to drive inflammation rather than resolve it.
Key studies
| Study | Design and population | Outcome | Grade |
|---|---|---|---|
| Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial2014 PMID 25041740 | Randomized, double blind, placebo controlled phase I/II trial, 4 weeksn = 34 Adults with hard to heal venous leg ulcers | LL-37 gel at 0.5 and 1.6 mg/mL twice weekly produced significantly faster ulcer healing than placebo; 3.2 mg/mL did not | Evidence: Human RCT evidence |
| Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial2021 PMID 34687253 | Randomized, double blind, placebo controlled phase IIb trialAdults with hard to heal venous leg ulcers | Primary endpoint not met in the full study population; a signal was reported in a subgroup with larger ulcers | Evidence: Human RCT evidence |
| A comprehensive summary of LL-37, the factotum human cathelicidin peptide2012 PMID 23246832 | Narrative reviewIn vitro, animal, and human observational data | Summarizes antimicrobial, immunomodulatory, wound healing, and pro inflammatory roles, including elevated LL-37 in psoriasis and rosacea | Evidence: Animal-only evidence |
Conditions studied
| Condition | Grade | Note |
|---|---|---|
| Wound healing | Evidence: Human RCT evidence | Small randomized trial of topical LL-37 in venous leg ulcers; not approved. |
| Immune support and immune deficiency | Evidence: Animal-only evidence | Human antimicrobial peptide with broad lab and animal activity; no human study of injected LL-37 for immunity. |
| Autoimmune disease | Evidence: No published evidence | LL-37 is implicated in psoriasis and lupus, so it is a theoretical risk in autoimmunity rather than a treatment. |
Is LL-37 legal in the United States?
FDA and compounding status
Not an FDA approved drug. LL-37 was placed on the FDA 503A Category 2 list (bulk substances with significant safety risks) in 2023 and was one of the peptides FDA now lists as withdrawn from 503A Category 2 (page current as of April 22, 2026) after the nominations were withdrawn. It was not among the peptides the Pharmacy Compounding Advisory Committee recommended for the 503A bulks list at its July 23 to 24, 2026 meeting, so it currently sits in neither category and most 503A pharmacies will not compound it. Not eligible for 503B outsourcing.
WADA status
WADA prohibited. Athletes subject to anti-doping testing should treat this as prohibited at all times unless the current prohibited list says otherwise.
Regulatory timeline
- FDA
FDA lists BPC-157 and 16 other peptides as withdrawn from 503A Category 2
FDA's Category 2 page, revised in April 2026 and current as of April 22, 2026, moved BPC-157, AOD-9604, CJC-1295, dihexa, DSIP, epitalon, injectable GHK-Cu, ipamorelin, KPV, LL-37, melanotan II, MOTS-c, PEG-MGF, selank, semax, thymosin alpha-1, and thymosin beta-4 fragment (TB-500) to a list of bulk drug substances nominated but withdrawn by their nominators. A withdrawn substance is no longer in 503A Category 2, but withdrawal is not an approval and does not place a substance on the 503A bulks list; a 503A pharmacy still needs a listing before it may compound it. Ipamorelin acetate remains in 503B Category 2. Seven of the withdrawn peptides (BPC-157, KPV, TB-500, MOTS-c, semax, epitalon, and DSIP) were taken to the Pharmacy Compounding Advisory Committee in July 2026.
- FDA
FDA places a batch of nominated peptides in 503A Category 2
In September 2023 FDA updated its 503A bulk drug substances category lists to place a group of nominated peptides in Category 2, which means FDA identified significant safety risks and the substances may not be used in 503A compounding while the evaluation continues. Kisspeptin-10 and ibutamoren (MK-677) were added on September 29, 2023 and remain in Category 2 on the FDA page current as of April 22, 2026. BPC-157, CJC-1295, ipamorelin, AOD-9604, dihexa, DSIP, epitalon, KPV, MOTS-c, selank, semax, melanotan II, LL-37, thymosin alpha-1, and thymosin beta-4 fragment (TB-500) were also placed in Category 2 under the 503A interim policy; that same page now lists them as nominated but withdrawn (see the April 2026 event). Hexarelin, PNC-27, and 5-amino-1MQ have never appeared on the FDA category lists.
What published studies of LL-37 used
Ranges below are reported from published studies and labeling only. PeptideAgent does not recommend doses or protocols.
Topical gel at 0.5 mg/mL or 1.6 mg/mL applied to the ulcer twice weekly for 4 weeks (Gronberg 2014; the same two concentrations were used in Mahlapuu 2021). No human dose exists for injected or systemic LL-37.
Routes reported
| # | Route |
|---|---|
| 1 | Topical gel on chronic wounds (clinical trials) |
| 2 | Subcutaneous injection (as sold, no human data) |
| 3 | Nebulized or intranasal (as sold, no human data) |
What are the side effects and interactions of LL-37?
Side effects
| # | Reported side effect |
|---|---|
| 1 | Topical trials: local wound reactions comparable to placebo at the two lower doses; the 3.2 mg/mL dose was not better than placebo and higher concentrations are cytotoxic in vitro |
| 2 | No systemic human safety data for injected LL-37 |
| 3 | Theoretical concern that LL-37 worsens autoimmune and inflammatory skin disease, because it is elevated in psoriasis and rosacea lesions |
| 4 | Injection site pain and flu like symptoms reported anecdotally |
Interactions
| # | Interaction |
|---|---|
| 1 | No human interaction studies exist |
| 2 | In vitro, LL-37 binds and neutralizes lipopolysaccharide and can complex with self DNA and RNA to activate plasmacytoid dendritic cells, which is the proposed mechanism in psoriasis; relevance to co-administered drugs is unknown |
Contraindications
| # | Contraindication |
|---|---|
| 1 | Psoriasis, rosacea, or lupus (theoretical, LL-37 is implicated in these diseases) |
| 2 | Pregnancy and breastfeeding (no data) |
| 3 | Competitive athletes subject to WADA testing (prohibited under S0) |
How do people access LL-37 legally?
Typical cost: Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. Not routinely available through licensed telehealth or compounding channels as of the last verified date.
Verified access options
Step 1
Not available as an FDA approved product.
Step 2
It is off Category 2 but not on the 503A bulks list, so a 503A pharmacy has no federal basis to compound it from bulk.
Step 3
Products labeled research use only are not lawful for human use and are not verified for purity.
Access paths are verified against public regulatory records and prescriber licensing. We never list unlicensed vendors.
Compare LL-37
What's actually offered, and what that means for you
Licensed compounding pharmacies, clinics, and telehealth prescribers openly offer many unapproved peptides, and prescribers write prescriptions for them. That does not make LL-37 lawful. LL-37 is not FDA approved and not on the 503A bulks list, so a pharmacy has no lawful basis to compound it. [4] [7]
Enforcement is uneven. FDA mostly acts through warning letters to compounders and online sellers, Category 2 safety listings, and import alerts that let it detain shipments, rather than stopping every pharmacy. State pharmacy boards oversee pharmacies day to day, and their rules differ. [7] [8] [9] [10] [11]
What changes for you
- No FDA review of the product: FDA does not check a compounded drug's safety, effectiveness, or quality before it is sold. [11]
- Identity, purity, sterility, and dose accuracy can vary from batch to batch. [7]
- Insurance rarely covers it, so you usually pay cash.
- For tested athletes, LL-37 is prohibited at all times on the WADA list, whatever the source. [6]
What to check
These checks lower some risks, but they do not make an unlawfully compounded product lawful or safe. Check for:
- A 503A pharmacy licensed in your state (your state board of pharmacy publishes license lookups). [11]
- A real evaluation by a licensed prescriber, not just an online form.
- A certificate of analysis for the specific batch.
Frequently asked questions
Is LL-37 legal in the United States?
It is not an FDA approved drug. FDA removed LL-37 from its 503A Category 2 list on April 15, 2026, which lifted the significant safety risk designation, but it was not among the peptides the July 2026 advisory committee (FDA's outside expert panel) recommended for the 503A bulks list, the list of ingredients pharmacies may use to compound drugs for individual patients. That leaves it in a gray zone where most compounding pharmacies will not fill it. Buying it as a research chemical for personal use is not lawful for human use. [4] [5]
Does LL-37 work for wound healing?
Topically, maybe. In a 34 patient randomized trial, LL-37 gel at 0.5 and 1.6 mg/mL healed venous leg ulcers faster than placebo over 4 weeks. A larger phase IIb trial of the same doses did not meet its primary endpoint in the full population. No trial has tested the injected form people buy online, so there is no evidence it heals anything when injected. [1] [2]
Does LL-37 fight infections in people?
Not demonstrated. LL-37 kills bacteria in the test tube and protects mice from infection, but no human trial has tested it as an antibiotic. Its antimicrobial activity in vitro is reduced by physiological salt and serum, which is one reason clinical development has focused on wounds rather than systemic infection. [3]
What are the side effects of LL-37?
In the topical trials, local effects at the two lower doses were similar to placebo, and the highest dose (3.2 mg/mL) lost its benefit, consistent with LL-37 being toxic to human cells at higher concentrations. There is no systemic safety data. LL-37 is overproduced in psoriasis and rosacea lesions and is thought to drive inflammation there, so people with those conditions have a theoretical reason to avoid it. [1] [3]
How is LL-37 taken?
In the clinical trials it was a gel applied to the ulcer twice a week for 4 weeks. Products sold online are usually lyophilized vials for subcutaneous injection, sometimes nebulized. No human study has used those routes, so no dose exists for them. [1] [2]
How much does LL-37 cost?
Products sold as research chemicals are not lawful for human use and are not tested for purity. It is not routinely offered by licensed telehealth or compounding channels. [4]
Is LL-37 banned by WADA?
Yes. LL-37 has no approval from any government health authority for human use, so it falls under section S0 (non-approved substances) of the WADA Prohibited List and is prohibited at all times. [6]
LL-37 vs thymosin alpha-1 for immune support: which has better evidence?
Thymosin alpha-1 is an approved drug in several countries and has randomized human trials in hepatitis B and as a vaccine adjuvant. LL-37 has only two topical wound trials and no systemic human data. Neither is FDA approved, and neither has evidence for general immune support in healthy people. [1] [3]
Decisions about starting, stopping, or combining any treatment belong with a licensed clinician who knows your history.
Sources
Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.
- [1]Gronberg 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 2014PubMed 25041740, 2014
- [2]Mahlapuu M et al. Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial. Wound Repair Regen 2021PubMed 34687253, 2021
- [3]Vandamme D et al. A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cell Immunol 2012PubMed 23246832, 2012
- [4]FDA: Bulk drug substances used in compounding under section 503A of the FD&C Act (links to the Category 1, 2, and 3 lists and the bulks list)FDA, 2026
- [5]FDA Pharmacy Compounding Advisory Committee meetings (July 2026 meeting on peptide nominations)FDA, 2026
- [6]WADA Prohibited List, section S0 non-approved substancesWADA, 2026
- [7]FDA: Certain bulk drug substances for use in compounding may present significant safety risks (Category 2)FDA
- [8]FDA: Compounding inspections, recalls, and other actions (warning letters to compounders)FDA
- [9]FDA warning letters database: July 30, 2019 letter to a 503A pharmacy that compounded BPC-157 acetate outside section 503AFDA, 2019
- [10]FDA Import Alert 66-41: Detention without physical examination of unapproved new drugs promoted in the U.S. (includes peptide entries)FDA
- [11]FDA: Compounding and the FDA, questions and answersFDA
Cite this page
Free to cite and quote with a link. Data is licensed CC BY 4.0 with attribution to PeptideAgent.
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PeptideAgent. (2026, September 22). LL-37: evidence, legality, and access. https://peptideagent.ai/peptides/ll-37- HTML link
<a href="https://peptideagent.ai/peptides/ll-37">LL-37: evidence, legality, and access</a>, PeptideAgent, updated September 22, 2026.