The Next Five: What We Actually Know About LL-37, GHK-Cu, Melanotan II, Dihexa, and PEG-MGF
Before the end of February 2027, the FDA reviews five more peptides. We checked the human data on each one. The result surprises both ways.
Important note: This article reviews scientific literature and a US regulatory process for informational purposes only. None of the five substances discussed is an approved drug in the EU or the US. We supply research substances for laboratory use, not for human consumption. Nothing here is a dosing recommendation, a protocol, a safety assurance, or legal advice. We carry three of the five substances in our catalog, which gives us an obvious interest in how this piece turns out. We wrote down every finding exactly as it appears in the source anyway, including where it is uncomfortable.
TL;DR: five substances, three completely different evidence classes
What's coming: Before the end of February 2027, the FDA's Pharmacy Compounding Advisory Committee will review five more peptides for the US Section 503A list: LL-37, GHK-Cu, Melanotan II, dihexa acetate, and PEG-MGF. A meeting date has not yet been published. The upside surprise: LL-37 is the only one of the five with a randomized phase IIb trial, in 148 patients. It showed no significant improvement versus placebo in the full study population. The downside surprise: For dihexa, the paper that made its mechanism of action interesting in the first place was retracted in April 2025. No clinical trial in humans is findable. The irony: Melanotan II has human data from the year 2000. A drug actually was approved from its own substance family, namely bremelanotide. Not because its pigmenting effect was removed, but because it went through a full approval process. What that means for the forecast: By the standard the FDA's reviewers applied in July 2026, more speaks against all five than for them. That said, it tells you little about how the vote will actually go, and why, is explained further below.
Cathelicidin-derived antimicrobial peptide (37 amino acids). Researched for innate immunity, antimicrobial activity, and wound-healing pathways. ≥99% HPLC purity with Janoshik CoA.
Naturally occurring copper tripeptide complex for skin regeneration and anti-aging research. Stimulates collagen synthesis, accelerates wound healing, and modulates 4000+ genes. Plasma levels decline with age, making it a key target in longevity research.
Tanning peptide that activates melanin production in the skin. Stimulates melanocyte receptors for natural UV-free pigmentation. Also researched for appetite regulation and libido effects.
Tissue repair, wound healing, and recovery peptides
What February 2027 is about
On July 23 and 24, 2026, the FDA's Pharmacy Compounding Advisory Committee (PCAC) reviewed seven peptides and recommended six of them for the Section 503A list. What was decided there, what was not, and why that is not an approval, is covered in our full report on the votes.
This article covers the second round. Five more substances come before the same committee: LL-37, GHK-Cu, Melanotan II, dihexa acetate, and PEG-MGF. The meeting is expected before the end of February 2027; as of August 2026, no date or location had been published.
We carry three of these five. Rather than wait for the committee's verdict, we looked up what human data actually exists for each substance. For none of the five is the answer what you would expect from the sales literature, and that cuts in both directions.
LL-37: the only one with a phase IIb trial, and it remained without a significant effect
LL-37 is the only one of the five to have gone all the way through a proper clinical development program. A Swedish company developed it as a topical wound treatment under the international nonproprietary name ropocamptide.
The first study came out positive. In a first-in-man study of 34 patients with hard-to-heal venous leg ulcers (Grönberg et al., Wound Repair and Regeneration, 2014), three concentrations were tested, 0.5, 1.6, and 3.2 mg/ml, each against placebo. For the two lower ones, the healing rate constants were roughly sixfold (0.5 mg/ml) and roughly threefold (1.6 mg/ml) above placebo. Of these, only the lowest dose was statistically significant (p = 0.003), the middle one was not (p = 0.088). For the highest dose, the publication reports neither of these two comparison values.
The larger study did not confirm it. The phase IIb trial HEAL LL-37 (Mahlapuu et al., Wound Repair and Regeneration, 2021) was double-blind, randomized, placebo-controlled, multicenter, and enrolled 148 patients. In the publication's own words: the efficacy analysis in the overall population showed no significant improvement in healing versus placebo. Significance only emerged in a post hoc analysis of a subgroup, namely patients with large wounds of 10 cm² or more. The authors themselves write that this urgently warrants a further, adequately powered study. Tolerability and safety were good at both dose strengths.
Why the post hoc subgroup does not rescue the trial
A post hoc subgroup analysis is formed after looking at the data, not defined in advance. It can generate a hypothesis for the next study, but it cannot substitute for a negative result in the full study population. The authors themselves say as much. Three of the authors were employed by the sponsor at the time of the study, and one is a minority shareholder, both disclosed in the publication.
For the February 2027 evaluation, there is a second point that regularly gets lost in the discussion: both trials studied topical application to an open wound. These studies provide nothing on injected use of LL-37 in humans. Anyone reading the wound-healing data as evidence of a systemic effect is reading in something that was never studied.
GHK-Cu: a single human trial, and it was negative on every objective endpoint
GHK-Cu is the substance among the five with the widest public name recognition, carried by the cosmetics market. Even so, the solid human evidence is thin, and it is consistently topical.
The randomized trial most frequently cited tested a topical copper tripeptide complex after CO2 laser skin resurfacing (Miller et al., Archives of Facial Plastic Surgery, 2006). After the procedure, patients were randomized to post-treatment with or without GHK-Cu, and blinded raters and computer analysis assessed erythema and wrinkling.
And now the result that the sales literature rarely cites alongside it. 13 patients completed the study. Computer analysis and blinded evaluators found no statistically significant difference between the groups in the resolution of erythema. All patients improved noticeably in wrinkles and skin quality, but no difference was found between the groups. One thing alone was significant, the questionnaire: patients who had used GHK-Cu rated their post-treatment skin quality higher (p = 0.04). The authors themselves summarize it as GHK-Cu producing no significant reduction in erythema, with objective evaluation finding no significant improvement in wrinkles or skin quality, but patient satisfaction being significantly higher.
That is the most solid human evidence this substance has: 13 people, objectively negative, subjectively positive. On top of that, it is a study of a topical post-treatment, not of an injection. We wrote up in detail how much that second distinction matters in GHK-Cu, topical or injected: intact human skin lets through barely any peptide or copper on its own, and the only independent pharmaceutical study we found needed microneedle pretreatment just to produce any meaningful uptake at all.
What that means for the nomination
The 503A list covers substances US pharmacies may compound on prescription. A nomination is evaluated for specific dosage forms and indications. Which dosage form GHK-Cu is being evaluated for this time was not publicly documented as of August 2026. Should it be the injectable one, human data on a topical preparation would only transfer in a limited way. The FDA reviewers flagged exactly this gap between the studied use and the requested use for several of the seven substances in July 2026.
Melanotan II: the only one with an actual safety record
Melanotan II is the special case among the five. It has human data, and it is the only one with an extensive body of modern literature, which consists almost entirely of harm reports.
The efficacy side is old and small. The pivotal study (Wessells et al., International Journal of Impotence Research, 2000) gave Melanotan II to 20 men with erectile dysfunction in a double-blind, placebo-controlled crossover design. 17 of 20 developed an erection without sexual stimulation, with a mean duration of RigiScan tip rigidity above 80 percent of 41 minutes. Increased sexual desire was reported after 13 of 19 Melanotan II doses versus 4 of 21 under placebo. Nausea and yawning were common.
The safety side is new and growing. The case report literature of recent years includes, among other things, rhabdomyolysis with renal failure and a renal infarction (CEN Case Reports, 2020), the question of oral mucosal malignant melanoma after nasal spray use (International Journal of Oral and Maxillofacial Surgery, 2025), five primary melanomas in situ in a patient with, among other exposures, melanotan use (JAAD Case Reports, 2026), and mucosal changes after 64 days of self-administration (Life, 2026). A Dutch review article summarizes the risks under the substance's popular name (Nederlands Tijdschrift voor Geneeskunde, 2022).
What case reports show, and what they do not
Case reports do not establish causality and have no denominator: you never learn how many people used the substance without an event. But they are the signal that safety assessments start from, and for Melanotan II they are more numerous and more current than the efficacy data. For a benefit-risk assessment, that is the least favorable configuration imaginable: the evidence of benefit is 25 years old and comes from 20 people, while the risk signal is fresh and growing.
And then there is the punchline that explains the case best. A drug has in fact been approved from the same substance class: bremelanotide, in the US since June 2019 under the name Vyleesi. And here it gets interesting, because the obvious conclusion is wrong: bremelanotide is not the molecule that had its pigmenting effect removed. The US prescribing information describes it as a nonselective melanocortin receptor agonist with the potency order MC1R, MC4R, MC3R, MC5R, MC2R, and notes that at therapeutic doses, binding to MC1R and MC4R is most relevant. MC1R is precisely the receptor that drives pigmentation, and it stands first in that order. Bremelanotide has been approved since June 21, 2019 for a narrowly defined indication, acquired, generalized hypoactive sexual desire disorder in premenopausal women. We carry this peptide as PT-141 in our research catalog.
Cyclic heptapeptide (bremelanotide) that acts as a melanocortin receptor agonist at MC3R and MC4R in the central nervous system. The active metabolite of Melanotan-II, studied for sexual-function endpoints via a central rather than vascular pathway.
So what separates bremelanotide from Melanotan II is, at any rate, not a removed pigmenting effect. It is the process: a defined indication, a defined dose, a clinical program that was completed, and prescribing information with its own warnings. That is exactly what Melanotan II lacks. A direct comparison of the two substances' receptor profiles cannot be derived from the prescribing information, since it describes only bremelanotide.
Dihexa: the paper that carried everything has been retracted
Dihexa is an orally bioavailable, brain-penetrant angiotensin IV analog that was discussed as a candidate against neurodegenerative disease in the 2010s. The attention it received rested at its core on a single paper: Benoist et al., Journal of Pharmacology and Experimental Therapeutics, 2014, which reported that the procognitive and synaptogenic effects of angiotensin IV-derived peptides depend on activation of the hepatocyte growth factor/c-Met system. That was the mechanism that turned dihexa from a curiosity into a candidate.
There is a retraction for this paper
In 2021, the paper first received an Expression of Concern (JPET 378(3):311). In April 2025, it was retracted (Retraction Notice, JPET 392(4):103567). PubMed has listed it as a "Retracted Publication" ever since. Anyone justifying dihexa today with the HGF/c-Met mechanism is relying on a retracted publication.
A PubMed search for clinical trials in humans on dihexa returns zero hits. What remains is preclinical work in rodents and a review article on the development of angiotensin IV analogs (Progress in Neurobiology, 2015).
We do not carry dihexa and never have. Anyone looking in the cognitive space for substances with at least some human literature is more likely to find it among the established nootropic peptides, whose data we wrote up in Semax and Selank, including the caveats that apply there too.
PEG-MGF: the thinnest file of the five
PEG-MGF, pegylated mechano growth factor, is a pegylated variant of a splice variant of IGF-1. The pegylation is meant to extend its half-life.
A PubMed search for PEG-MGF returns a handful of hits, and none of them is a clinical trial of this substance. What turns up is basic research on pegylated IGF-1 conjugates (Journal of Controlled Release, 2018) and review articles on the IGF-1 system in general.
The only current paper that even names PEG-MGF places it exactly where it stands: a review in Frontiers in Endocrinology from June 2026 covers performance-enhancing peptides of the GH-IGF-1 axis that are "marketed as research substances," and explicitly describes the gap between clinical evidence and self-administration. PEG-MGF appears there as an example of a substance with an established user base and no clinical evidence base at all.
Why that is particularly difficult for a compounding process
A pegylated protein is analytically demanding to characterize: the length and position of the PEG chain help determine both effect and immunogenicity. In July 2026, the FDA reviewers flagged exactly this kind of characterization for several substances, in some cases even at the level of distinguishing free base from acetate. For a pegylated conjugate with no published clinical data, that bar sits considerably higher.
The stocktake in one table
- Best human evidence
- Phase IIb, n=148, no significant improvement in the full study population (2021); first-in-man study, n=34 (2014)
- Form studied
- topical, open wound
- Safety signal
- well tolerated in the trials
- Best human evidence
- one randomized trial, n=13 completers, objectively negative, only the patient questionnaire significant (2006)
- Form studied
- topical, post-treatment
- Safety signal
- no safety finding reported from this study
- Best human evidence
- crossover study, n=20, erectile dysfunction (2000)
- Form studied
- injected
- Safety signal
- extensive current case report literature
- Best human evidence
- no clinical trial in humans findable
- Form studied
- none
- Safety signal
- mechanism paper retracted
- Best human evidence
- no clinical trial in humans findable
- Form studied
- none
- Safety signal
- no clinical literature found
What the July pattern predicts
Now for the forecast, laid out so you can check the arithmetic instead of having to take it on faith.
The standard is public: for the seven substances in July 2026, the FDA's scientific reviewers recommended in their briefing documents not to add all seven of them. The reasons recurred: too little or no human data, studies in dosage forms other than the one requested, inadequate characterization of the substance, immunogenicity questions. We read those documents and wrote up the citations in our review of the FDA briefings.
Apply the same standard to the five, and a very clear picture emerges:
- Dihexa and PEG-MGF have no findable clinical trial in humans. For dihexa, the central preclinical paper is also retracted. By the July standard, a negative reviewer recommendation is the most obvious expectation here.
- GHK-Cu has exactly one randomized human trial, and it came out negative on every objective endpoint. Whether the dosage form adds a further mismatch is open, because the form being evaluated is not publicly documented.
- LL-37 has the formally best study, and of all things, that one came up without a significant effect in the full study population. For the question of sufficient efficacy evidence, that is not an advantage over having no study at all, it is a documented negative result.
- Melanotan II has an old, small efficacy record and a growing risk signal. For a benefit-risk assessment, that is the hardest starting position of the five.
That is the forecast for the reviewers. It is not the forecast for the vote. And that difference is the actual point.
The emideltide paradox: evidence depth does not predict the outcome
In July, the committee overruled its own reviewers on six of seven substances. The one where it followed the reviewers and rejected the substance was emideltide, better known as DSIP. Of the seven, emideltide had the deepest human record, with studies going back to 1981. Waved through instead was, among others, MOTS-c, for which the FDA reviewers found no human studies at all.
Anyone trying to infer voting behavior from evidence depth would have been exactly wrong in July. So for February 2027 we predict a likely reviewer stance, and explicitly no prediction about how the vote will turn out. Anyone offering you such a prediction is selling you a coin and calling it a compass.
What this practically means for European readers
In short: legally, nothing. Informationally, a lot.
The process is a US compounding process. It decides whether American pharmacies may compound preparations from these substances on prescription. It is not a drug approval, and it does not affect the European classification. All five substances remain unapproved research substances in the EU. They stay that way with us too: laboratory use, not for human consumption.
The informational value lies elsewhere. By February 2027, the FDA reviewers will publish a public, written, adversarially structured evidence assessment for each of these five substances. For dihexa and PEG-MGF, that will be the first coherent regulatory assessment of their data ever. That is useful regardless of how the vote turns out, and it has a longer shelf life than any headline about the outcome.
What stays the same for us
As long as the regulatory status is open, batch documentation remains the decisive factor, not the headline. For every batch we carry, there is a certificate of analysis from a third-party lab, viewable on our CoA page. A vote by an advisory committee changes nothing about what is in a vial. An HPLC run does.
Substances from the February round that we carry
Cathelicidin-derived antimicrobial peptide (37 amino acids). Researched for innate immunity, antimicrobial activity, and wound-healing pathways. ≥99% HPLC purity with Janoshik CoA.
Naturally occurring copper tripeptide complex for skin regeneration and anti-aging research. Stimulates collagen synthesis, accelerates wound healing, and modulates 4000+ genes. Plasma levels decline with age, making it a key target in longevity research.
Tanning peptide that activates melanin production in the skin. Stimulates melanocyte receptors for natural UV-free pigmentation. Also researched for appetite regulation and libido effects.
From the July round
Gastric pentadecapeptide (15 amino acids) known for exceptional tissue repair properties. Promotes wound healing, angiogenesis, and cytoprotection across tendons, muscles, gut, and nerves. Over 30 years of preclinical research.
Full-length 43-amino-acid Thymosin Beta-4, a naturally occurring repair protein, independently confirmed by a third-party CoA from Janoshik. Promotes cell migration and new blood vessel formation for systemic tissue healing. Especially researched for muscle, tendon, and cardiac repair.
Anti-inflammatory tripeptide derived from alpha-MSH (positions 11-13). Inhibits NF-kB signaling, supports gut barrier integrity, and shows antimicrobial activity. A targeted approach to inflammation research without broad immunosuppression.
Bottom line
The five substances of the February round share one thing in common, and it is not what you would expect: for none of them does the human evidence support the expectation the market has of it. Not for LL-37, because the large trial remained without a significant effect in the full study population. Not for GHK-Cu, because its only human trial was negative on every objective endpoint. Not for Melanotan II, because the safety file now outweighs the efficacy file. Not for dihexa and PEG-MGF, because no clinical trial in humans can be found.
That is not an argument against research on these substances. It is an argument for aligning expectations with what was actually studied. When the committee meets, the headline will be how it decided. The more useful part is the assessments published before that.
Sources
- Grönberg A, Mahlapuu M, Ståhle M, Whately-Smith C, Rollman O. 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 and Regeneration, 2014. PMID 25041740. https://pubmed.ncbi.nlm.nih.gov/25041740/
- Mahlapuu M, Sidorowicz A, Mikosinski J, 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 and Regeneration, 2021;29(6):938-950. PMID 34687253. https://pubmed.ncbi.nlm.nih.gov/34687253/
- Miller TR, Wagner JD, Baack BR, Eisbach KJ. Effects of topical copper tripeptide complex on CO2 laser-resurfaced skin. Archives of Facial Plastic Surgery, 2006. PMID 16847171. https://pubmed.ncbi.nlm.nih.gov/16847171/
- Wessells H, Levine N, Hadley ME, Dorr R, Hruby V. Melanocortin receptor agonists, penile erection, and sexual motivation: human studies with Melanotan II. International Journal of Impotence Research, 2000. PMID 11035391. https://pubmed.ncbi.nlm.nih.gov/11035391/
- Peters B, et al. Melanotan II: a possible cause of renal infarction: review of the literature and case report. CEN Case Reports, 2020. PMID 31953620. https://pubmed.ncbi.nlm.nih.gov/31953620/
- Yassin Alsabbagh A, et al. Melanotan II nasal spray: a possible risk factor for oral mucosal malignant melanoma? International Journal of Oral and Maxillofacial Surgery, 2025. PMID 40210573. https://pubmed.ncbi.nlm.nih.gov/40210573/
- Vadner DJ, et al. Five primary melanomas in situ in a patient with recent tanning bed use, melanotan exposure, and anabolic hormone use. JAAD Case Reports, 2026. PMID 42328529. https://pubmed.ncbi.nlm.nih.gov/42328529/
- Bonchev A, et al. Changes in Oral Mucosa Associated with Melanotan II Injections: A Case Report. Life (Basel), 2026. PMID 41752902. https://pubmed.ncbi.nlm.nih.gov/41752902/
- Benoist CC, Kawas LH, Zhu M, et al. The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-Met system. Journal of Pharmacology and Experimental Therapeutics, 2014. Retracted. PMID 25187433. https://pubmed.ncbi.nlm.nih.gov/25187433/
- Retraction notice for Benoist et al. 2014. Journal of Pharmacology and Experimental Therapeutics, April 2025;392(4):103567. PMID 40312093. https://pubmed.ncbi.nlm.nih.gov/40312093/
- Wright JW, Kawas LH, Harding JW. The development of small molecule angiotensin IV analogs to treat Alzheimer's and Parkinson's diseases. Progress in Neurobiology, 2015. PMID 25455861. https://pubmed.ncbi.nlm.nih.gov/25455861/
- Dominikowski A, Rękoś Z, Olejarz M, et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Frontiers in Endocrinology, June 2026;17:1822475. PMID 42395176. https://pubmed.ncbi.nlm.nih.gov/42395176/
- VYLEESI (bremelanotide injection), US prescribing information, initial approval 2019, Section 12.1 Mechanism of Action (potency order MC1R, MC4R, MC3R, MC5R, MC2R) and Indications and Usage. FDA. https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/210557s000lbl.pdf (full text also on DailyMed: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f1d0c1b5-2f39-4bad-a6a4-0066e3ad5dcf)
- July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. FDA. https://www.fda.gov/advisory-committees/advisory-committee-calendar/july-23-24-2026-meeting-pharmacy-compounding-advisory-committee-07232026
Note on our catalog: All peptides offered at peptidesdirect.io are research substances for laboratory use only. They are not intended for human or animal consumption, not for the diagnosis, treatment, or prevention of disease, and hold no drug approval in the EU.
Research context for English-speaking buyers
Most of our English-speaking customers ship to the UK, Ireland, Malta or other English-as-second-language EU territories. The regulatory picture differs per country.
- Relevant authorities
- MHRA (UK, post-Brexit), HPRA (Ireland, EU-aligned), FDA Section 503A bulks list (US, restricted Cat 2 status of several peptides as of 2026)
- Customs and VAT
- EU shipments include 19% VAT; UK shipments after Brexit are now extra-EU and may attract UK VAT plus a handling fee at import
- Typical shipping window
- EU 2-4 working days, UK 4-7 working days, other international 7-14 working days, depending on customs
Research-grade peptides shipped from our EU warehouse are sold for laboratory use only and are not authorised for human or veterinary therapeutic application in any of the destination jurisdictions. US customers should be aware that the FDA Section 503A bulks list classification (and the April 2026 reclassification of twelve compounds) only governs compounding pharmacies, not direct-to-researcher imports for non-clinical work. UK buyers should declare the consignment on import and may be asked for a research justification by HMRC. We provide a CoA per batch identified by colour code rather than serial number; customs sometimes asks for this document when clearing the parcel.