The Antimicrobial Peptide

LL-37

Also known as Cathelicidin · hCAP18 fragment · Ropocamptide

At a glance

What it is: Human antimicrobial peptide. FDA wrote a stronger warning for it than for any peer.

Evidence: Small human studiesHow the tiers workOne controlled human trial exists and it is topical. Why this tier

Half-life: Not established in available literature
Routes: Topical, Subcutaneous
Category: Immune, Healing
FDA: Advisory vote planned; As of 3 August 2026. What that means
WADA: We do not state a status
Amino acids: 37

Not schedulable in Claritide. Our sources publish no dosing figure for LL-37, so there is nothing to build a schedule from.

Evidence

Why this tier

One controlled human trial exists and it is topical. HEAL LL-37 (Promore Pharma, Phase 2b, double-blind, randomised, placebo-controlled) treated 144 patients with hard-to-heal venous leg ulcers using topical ropocamptide plus compression: there was no statistically significant difference in the total study group. In the subgroup with large ulcers of 10 cm² or more, complete healing was 28.8% against 8.1% on placebo, which was significant. Injected LL-37 has no human-trial support and there is no validated human injection dose.

Overview

What it is

LL-37 is the human cathelicidin antimicrobial peptide, a real part of innate immunity with direct antimicrobial and pro-angiogenic activity. Its one controlled trial is topical, in venous leg ulcers, and it failed in the total study group while succeeding in a large-ulcer subgroup. FDA wrote a stronger safety line for LL-37 than for any other peptide on its withdrawn table, and almost nobody quotes it.

Mechanism

How it works

LL-37 is the active fragment released from hCAP18, the only cathelicidin humans make. It works in three ways that are hard to separate. It is directly antimicrobial: the peptide is amphipathic and cationic, so it inserts into and disrupts negatively charged bacterial membranes. It orchestrates the innate immune response, recruiting and activating immune cells and modulating cytokine output rather than simply amplifying it. And it is pro-angiogenic, which is where the wound-healing interest comes from. That last property is also where the caution comes from: pro-angiogenic signalling is not selective about what tissue it feeds.

Dosing

Commonly researched ranges

These are figures reported in published literature and practitioner protocols: a commonly researched range, not a recommendation. Claritide does not tell you what to take.

Topical trial concentrations (HEAL LL-37, Phase 2b)0.5–1.6 mg
Trial concentrations in mg/mL, applied with compression therapy
The two arms tested were 0.5 mg/mL and 1.6 mg/mL, applied to the wound bed twice weekly, roughly 12.5 and 40 micrograms per square centimetre. The lower concentration outperformed the higher one, consistent with an earlier dose-response study, and a 3.2 mg/mL arm was dropped for local reactions. These are strengths of a solution, not amounts anybody draws, so Claritide offers no dose figure to choose for LL-37 at all: there is no honest way to print a concentration in a box that means milligrams.

Phase	Amount	Frequency	Timing	Note
Topical trial concentrations (HEAL LL-37, Phase 2b)	0.5–1.6 mg	Trial concentrations in mg/mL, applied with compression therapy	Not established in available literature	The two arms tested were 0.5 mg/mL and 1.6 mg/mL, applied to the wound bed twice weekly, roughly 12.5 and 40 micrograms per square centimetre. The lower concentration outperformed the higher one, consistent with an earlier dose-response study, and a 3.2 mg/mL arm was dropped for local reactions. These are strengths of a solution, not amounts anybody draws, so Claritide offers no dose figure to choose for LL-37 at all: there is no honest way to print a concentration in a box that means milligrams.

Cycle guidance: No cycling schedule exists. The only controlled human study is a fixed topical course given alongside compression therapy.
Goals: Immune, Recovery

Legal standing

Where this sits with the FDA

Dated, sourced, and separate from whether it works. Removal from a warning list is not permission to compound.

Advisory vote plannedas of 3 August 2026 · US

FDA 503A bulks · nomination withdrawn; FDA says it will hold an advisory committee meeting on it before the end of February 2027

FDA says it will hold an advisory committee meeting on LL-37 before the end of February 2027, alongside GHK-Cu, Melanotan II, dihexa acetate and PEG-MGF. Removal from Category 2 is not permission: it is not lawfully compoundable today. Read that alongside FDA’s own Category 2 safety text for this compound, which is the strongest it wrote for anything on the withdrawn table.

Last change · 22 April 2026 · Cathelicidin LL-37 was among the 12 peptides removed from Category 2, announced 15 April 2026 and effective 22 April 2026.

Primary source

How it got here

15 April 2026
FDA announced a future Pharmacy Compounding Advisory Committee meeting to discuss Cathelicidin LL-37, alongside GHK-Cu, Melanotan II, dihexa acetate and PEG-MGF, with its time and place still to be scheduled.
22 April 2026
FDA removed 12 peptide bulk substances from Category 2 after the nominators withdrew their nominations. Announced 15 April 2026, effective 22 April 2026. Removal from Category 2 is not permission to compound.
28 February 2027
FDA says its Pharmacy Compounding Advisory Committee will meet before the end of February 2027, on a date not yet set.

An advisory vote is not law. In July 2026 an FDA advisory committee voted in favour of adding several peptides to the 503A bulks list, over the explicit recommendation of FDA’s own scientific reviewers, who recommended against all seven. FDA would still have to write a rule, and it has not proposed one or given a date. None of these compounds is lawfully compoundable today.Note what FDA actually assessed: BPC-157 for ulcerative colitis, TB-500 for wound healing, KPV for wound healing and inflammatory conditions, MOTS-c for obesity and osteoporosis, Epitalon for insomnia, Semax for cerebral ischaemia, migraine and trigeminal neuralgia. Whatever emerges from rulemaking will be scoped to those indications.

Sport

WADA status

The 2026 Prohibited List entered force on 1 January 2026.

We do not state a status

Not named on WADA’s 2026 Prohibited List. Its S0 section also bans drugs it does not name, when no government health authority currently approves them for human treatment. We found no such approval for LL-37 or its drug form, ropocamptide. USADA, the US anti-doping agency, warns that many experimental peptides are prohibited in sport. So athletes should treat LL-37 as likely prohibited and check with their federation before competing.

The FDA reclassification has no effect whatsoever on WADA status.

Reconstitution

Mixing recipes our sources document

Concentration (mg/mL) = vial mg ÷ diluent mL. On a U-100 barrel, 1 unit = 0.01 mL.

Not established in available literature. Use the calculator with the figures printed on your own vial.
Open the calculator

Expectations

Week by week

What our material describes people reporting. Individual responses vary widely.

Not established in available literature.

Tolerability

Side effects

Grouped by how often our sources report them. Percentages appear only where a published trial figure exists.

Rare

Detrimental effects on male reproduction (nonclinical)From FDA’s own Category 2 entry for cathelicidin LL-37: "Nonclinical research findings suggest detrimental effects on male reproduction and that this drug can be protumorigenic in some tissues." That is a materially stronger warning than FDA wrote for any other peptide on the withdrawn table.
Protumorigenic in some tissues (nonclinical)Same FDA entry. Pro-angiogenic and pro-proliferative signalling does not distinguish between tissue you want repaired and tissue you do not.

Safety

Contraindications and interactions

Do not use if

Cancer history or active malignancy: FDA states nonclinical findings suggest LL-37 can be protumorigenic in some tissues
Trying to conceive: FDA states nonclinical findings suggest detrimental effects on male reproduction
There is no validated human injection dose. Injected LL-37 for systemic immune or infection use has no human-trial support of any kind

Interactions

Not established in available literature.

Absence from this list does NOT mean safety. It means lack of research.

Handling

Storage and cost

Storage: Our sources publish no vial and diluent pairing and no beyond-use window for LL-37. The evidenced formulation is a topical preparation used in a trial setting.
Cost: Not established in available literature

Combinations

Stacks with

Only pairings our own material actually documents. Stacking is the least evidence-based part of this field.

Thymosin alpha-1The Immune Modulator KPVThe Inflammation Tripeptide

Deep dive

LL-37 in full

The sentence nobody quotes

FDA's Category 2 entry for cathelicidin LL-37 reads: "Nonclinical research findings suggest detrimental effects on male reproduction and that this drug can be protumorigenic in some tissues."

That is a materially stronger warning than FDA wrote for any other peptide on the withdrawn table. It is publicly available, it is in a document people cite for other purposes, and it is essentially absent from every page selling LL-37.

It also has a coherent mechanistic story behind it. LL-37 is pro-angiogenic and pro-proliferative. Those signals do not distinguish between tissue you want repaired and tissue you would rather not feed.

What LL-37 is

The active fragment released from hCAP18, the only cathelicidin the human body makes. It is a genuine component of innate immunity and it does three things at once: it disrupts bacterial membranes directly, it orchestrates the innate immune response by recruiting and modulating immune cells, and it promotes angiogenesis.

The one real trial: topical, and only in a subgroup

HEAL LL-37, run by Promore Pharma, Phase 2b, double-blind, randomised and placebo-controlled: topical ropocamptide plus compression therapy in hard-to-heal venous leg ulcers. 144 patients across 0.5 mg/mL, 1.6 mg/mL and placebo.

No statistically significant difference in the total study group. That is the headline result of the only controlled human trial of this compound, and it is negative.

In the pre-specified subgroup of large ulcers, 10 cm² and above, complete healing was 28.8% against 8.1% on placebo, which was significant. A subgroup finding in a trial that missed overall is a hypothesis for the next study, not a conclusion.

One detail worth carrying: the 0.5 mg/mL arm outperformed the 1.6 mg/mL arm, consistent with an earlier dose-response study. More was not better. That pattern shows up repeatedly in this library and it is worth internalising as a default expectation rather than a curiosity.

Injected LL-37 has nothing behind it

A Phase 1 gave intratumoral LL-37 into cutaneous melanoma metastases and reported it tolerable with a variable biological response. That is the extent of the injectable human record, and it is a local injection into a tumour, not a systemic immune protocol.

Trial-registry searches for LL-37 return mostly observational studies measuring endogenous LL-37 levels in relation to vitamin D status: biomarker research, not interventional trials. There is no validated human injection dose, and we publish an empty range for the injectable route on purpose.

The regulatory story is the opposite of what circulates

Two things get reported backwards about LL-37, and both matter.

It was not left behind while other peptides were liberalised. Cathelicidin LL-37 was among the 12 peptides removed from Category 2 on 15 April 2026, effective 22 April. FDA says it will hold an advisory committee meeting on it before the end of February 2027, alongside GHK-Cu, Melanotan II, dihexa acetate and PEG-MGF.

And removal from Category 2 is still not permission. It is not lawfully compoundable today. All the removal did was take away the "may present significant safety risks" designation, the same designation that carried FDA's male-reproduction and protumorigenic language. Losing the label does not undo the finding.

References

Sources

1
Mahlapuu et al., 2021 · HEAL LL-37 Phase 2b in venous leg ulcers, Wound Repair Regen 29(6):938–950
Source
2
FDA · Certain bulk drug substances for use in compounding that may present significant safety risks (Category 2 entry for cathelicidin LL-37)
Source
3
FDA · Meeting of the Pharmacy Compounding Advisory Committee, to be held before the end of February 2027, on cathelicidin LL-37, GHK-Cu, dihexa acetate, Melanotan II and PEG-MGF (content current as of 15 April 2026)
Source
4
Frier Levitt · FDA peptides do-not-compound list update, 2026
Source
5
Superpower · LL-37 guide
Source
6
Grönberg et al., 2014 · topical LL-37 in hard-to-heal venous leg ulcers, the 0.5 / 1.6 / 3.2 mg/mL dose-response study (dose review, 2026-08-17)
PMID 25041740 Source

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