LL-37 Peptide Dosage, the Trial That Missed Its Own Endpoint, & FDA Status
The one peptide on this site your own body already makes: LL-37 is released from wounded and infected skin as part of innate immune defense, and it's also the best-studied peptide on this site by completed human trial count. A small early trial found it significantly sped healing of hard-to-heal leg ulcers. Its own larger, confirmatory follow-up trial then missed its primary endpoint, and FDA's compounding safety file on it lists a possible tumor-promoting signal from nonclinical data. Real evidence and a real caution, in the same molecule.
Reviewed by the PepGuard team · Last reviewed Jul 28, 2026
37-residue cationic antimicrobial peptide, the active C-terminal fragment of human cathelicidin (hCAP18) · also sold as Cathelicidin LL-37, hCAP18 (LL-37 fragment)
Photo: engin akyurt / UnsplashReal trial doses, for a route almost nobody sells it as.
Both completed human trials tested a topical wound solution. The mcg/day injectable protocol is a vendor invention.
| What's cited | Range |
|---|---|
| Phase I/IIa trial dose (topical, n=34, venous leg ulcers) | 0.5-1.6 mg/mL solution, applied twice weekly directly to the wound bed for 4 weeks |
| Phase IIb confirmatory trial dose (topical, n=148) | Same 0.5 and 1.6 mg/mL concentrations, twice weekly for 13 weeks |
| Highest concentration trialed | 3.2 mg/mL, showed no improvement over placebo |
| Vendor-cited self-injection protocol | 100-200 mcg subcutaneous, once daily, a route and dose no published human trial has ever tested |
Unlike most peptides on this site, real completed human trials do exist for LL-37, but they tested a topical wound-dressing solution applied directly to open venous leg ulcers, not an injectable. The figures below separate what the trials actually tested from the mcg/day self-injection protocols vendors invented for a route of administration no trial has used.
A real trial worked. The trial built to confirm it didn’t.
In 2014, a randomized, placebo-controlled trial gave 34 patients with hard-to-heal venous leg ulcers one of three topical LL-37 concentrations, twice weekly, for four weeks. The 0.5 mg/mL group healed at roughly six times the rate of placebo (p = 0.003), with a 68% decrease in mean ulcer area. That's a real, statistically significant, peer-reviewed result, rarer for a research peptide than almost anything else on this site.
In 2021, the confirmatory follow-up scaled that same protocol to 148 patients across multiple centers, using the same 0.5 and 1.6 mg/mL doses, for 13 weeks. Across the full study population, it did not find a significant improvement in healing. A positive signal only appeared in a post-hoc subgroup, patients with wounds of at least 10 cm², a comparison the trial wasn’t statistically powered to make. That's not a reason to dismiss LL-37 outright, small early trials succeed and fail to replicate at scale for all kinds of reasons, but it is a reason to be precise about what “LL-37 works for wound healing” actually rests on: one small positive trial, and one larger trial that didn’t confirm it on the terms it set for itself.
Clean in two trials. Flagged once by FDA, for a different reason.
The completed trials found no significant adverse events. A separate FDA safety review flagged something the trials weren’t designed to catch.
| Signal | Frequency | Context |
|---|---|---|
| Local wound-site reaction (from the actual topical trials) | rarely reported | Both completed RCTs reported no significant local or systemic adverse events versus placebo, at any tested concentration. |
| Effects of subcutaneous injection or systemic dosing | unknown / not studied | No trial has tested LL-37 by injection. Every completed human study applied it topically, directly to an open wound. |
| Pro-tumorigenic or reproductive-system effects | unknown / not studied | FDA's own compounding safety review cites nonclinical findings suggesting this peptide can be protumorigenic in some tissues and harmful to male reproduction. The completed human wound trials didn't run long enough, or measure these outcomes, to confirm or rule this out in people. |
| Role in inflammatory skin disease (rosacea) | commonly reported | Abnormal processing of the body's own LL-37 is an established driver of rosacea inflammation (Yamasaki et al., 2007), a concern about dysregulated endogenous LL-37, distinct from giving exogenous peptide, but relevant context for a molecule marketed for skin repair. |
Not FDA-approved. Previously flagged by FDA for significant safety risks, then withdrawn from that list; currently absent from all three 503A nomination categories.
FDA's compounding safety review once placed "Cathelicidin LL-37" in Category 2, "Bulk Drug Substances that Raise Significant Safety Risks," citing nonclinical findings that suggested "detrimental effects on male reproduction" and that the drug "can be protumorigenic in some tissues," on top of general immunogenicity and impurity concerns common to compounded peptides. That listing has since moved to FDA's "nominated but withdrawn" list, meaning it's no longer an active Category 2 flag, and checked against the current 503A bulk substances nomination list (updated May 14, 2026), LL-37 doesn't appear in Category 1, 2, or 3 at all. Withdrawn from a safety-risk list isn't the same as cleared: the underlying nonclinical findings that triggered the flag in the first place are still on FDA's record, they're just not currently attached to an active nomination.
Every claim above, traced back.
Both wound-healing RCTs, the foundational rosacea mechanism paper, and FDA’s own compounding safety file. Click through and check them yourself.
LL-37 questions, answered.
The evidence is mixed, in an unusually well-documented way. A small 2014 trial (34 patients, hard-to-heal venous leg ulcers) found a significant, roughly sixfold healing-rate improvement at a 0.5 mg/mL topical dose. The larger 2021 confirmatory trial (148 patients, same doses) did not find a significant improvement across the full study population; a positive signal only showed up in a post-hoc, non-powered subgroup of patients with larger wounds. The early positive result didn't fully replicate at scale.
Neither, currently. It's not FDA-approved for any use. FDA's compounding safety office previously listed "Cathelicidin LL-37" in Category 2 (significant safety risks), citing nonclinical signals for tumor-promoting effects and male reproductive harm, before that nomination was withdrawn. As of the current (May 14, 2026) 503A list, LL-37 doesn't appear in any of the three nomination categories, meaning there's no active compounding review track either way.
Not according to any published trial. Both completed human RCTs applied LL-37 topically, as a solution on an open wound. No study has tested subcutaneous injection, so the mcg-based self-injection protocols sold by vendors have no trial behind them, for safety or for effect.
Two separate, real findings, worth not conflating. FDA's safety file on LL-37 cites nonclinical data suggesting the peptide can be protumorigenic in some tissues, a caution about the substance itself. Separately, published research shows that when the body's own LL-37 is abnormally processed, it's a documented driver of rosacea inflammation. Both are real, but neither comes from a study of injecting or applying additional LL-37 to a healthy person.
0.5 mg/mL or 1.6 mg/mL, applied topically twice weekly directly to a wound, is what the two completed RCTs actually tested, not a mcg/day systemic dose. A higher concentration tested (3.2 mg/mL) showed no benefit over placebo. That's real trial data for a topical wound application, not a validated dose for any other use.
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